PF: Summoner - Query

[Man With Dog]

Morning All,

I have posted recently regarding a character to play in our current PF game and am thinking that Summoner is the way to go. After alot of suggestions and possibilities this is a class i havent played before and wouldnt mind testing it out.

We have two arcane casters in the party currently with a witch and Magus but i think this is vastly different enough to fill completely different aspects.

I have read through parts of the Summones Handbook that was on here and wanted to check wit hthe playground on a couple of things.

Is there any type of Eidolon that works better than others?
(or is it simply, they work best in different aspects based upon what i want to achieve?)
Summoner or Sythesist or another?
What is the best type of Eidolon build to go with damage dealing?
I was looking at the Half Elf as a race due to the 1/4 evo points per level... suitable idea?

Currently running at level 6 for any idea's people are thinking of...

[Frog of War]

We have two arcane casters in the party currently with a witch and Magus but i think this is vastly different enough to fill completely different aspects.

This should be just fine for the party. As a summoner, you'll be filling more of a tank role than a pure-caster sort of role. A witch is good at debuffs, a magus is good at DPS, and you're good at buffs and summoning critters to soak up damage and distract monsters from the smushy PCs. That all seems to mesh well IMO.


Is there any type of Eidolon that works better than others?
I'm assuming you're asking about the different base forms? It depends on what sort of build you want your eidolon to have. One popular (and probably the highest DPS) build is an eidolon using manufactured weapons. For this you want to start with the bipedal form. If you're focusing on natural weapons, you may want to consider the quadruped form. You could give it one big powerful bite, a full attack with two claws and a bite after a charge with pounce, perhaps even more bites if you give it more heads, you get the idea.


Summoner or Sythesist or another?
The plus side of being a synthesist is that it deals with one of the biggest drawbacks of being a summoner: you are squishy, and if you get squished, your eidolon goes poof! However, it also removes one of the biggest benefits of being a summoner, which is that while your eidolon is fighting using its actions, you can be buffing it or your party with your actions. Synthesists have to share their actions with their eidolon.

I'm not sure if by "summoner" you mean the vanilla summoner, or the master summoner archetype, which is pretty good. Being able to spam Summon Monster while your eidolon is out is a good deal. But if you go that route, make sure to be well prepared: If you take forever with your turn because you have to look up all the creatures you summon or because you're not exactly sure what their abilities do, your GM will hate you, as may the other players.


What is the best type of Eidolon build to go with damage dealing?
Bipedal eidolon with lots of arms, lots of weapons. It'll eat through all your money just to keep it well-equipped though.



I was looking at the Half Elf as a race due to the 1/4 evo points per level... suitable idea?
Yes, unless you go with the master summoner archetype or another with a weaker eidolon.


Make sure one way or another that you utilize the Summon Monster spells at your disposal: there are a lot of monsters on that list (especially Summon Monster III, which you should have at 6th) that have some very useful spell-like abilities.

[Man With Dog]

Thanks for the response - and i did mean base form yes.

As for weapons - eventhough the level is 6 i wont have access to hardly any money and few pieces of weaponry so i wont be able to massively kit out a hugely armed eidolon with much other than maybe masterwork weapons for a little bit.

As i cant read the srd from work - how many evolutions would i get as a half elf - level 6. I know i get an extra evolution for being past level 4.
Just wondering what i can equip a level 6 with and i dont mind the idea of being a synthesist, makes me a little harder to take out.
Dont mind the summoner at all really - they seem pretty useful in most roles.

Is there any role a summoner excels more than another?

[CreganTur]

My group has a summoner in it and he's our uber-charger. The only spells he ever casts are Haste and the occacional wall of fire.

He went with the claw monster design- quadraped, 4 claws, pounce, and rend. He's also playing as a gnome so he was able to use it as a mount from the very beginning. His weapon of choice is a lance, for obvious reasons.

[Person_Man]

It a potent Tier 2 class that's exceedingly difficult to mess up. You'll be fine no matter what you do.

[Novawurmson]

It a potent Tier 2 class that's exceedingly difficult to mess up. You'll be fine no matter what you do.

While I agree heartily with the "Summoner is tier 2" and feel that the Summoner's numerical bonuses need to be adjusted, it is possible to make a semi-useless eidolon; a first-time player in my group ended up giving his Eidolon a bunch of minor spellcasting ability (Ray of Frost 1/day! Woo!) and some other mostly useless evolutions and had a rough time for the first level or so. Of course, then he leveled up and got to change all of his evolutions (and I nudged him towards Saph's guide), and his eidolon went from "useless" to "unkillable by anything in his CR and decent damage."

[Man With Dog]

I wouldnt mind idea's that pushed me towards unkillable or a killing machine - or in fact - both would be even better.
Obviously.

I am guessing isnt so much what base you start with other than deciding what yuo want it to do?
Saph's guide seems to sum most of it up pretty well.

[Man With Dog]

I have been looking through the Eidolons evolutions and such this morning.

I figure if i go Half Elf - i get 10 evolution points (9 from level - 1 from Half Elf alternate race ability)
Would anyone out there be willing to aid me in building the Eidolon of my dreams? I am looking for either a Tank Eidolon or a Damage Eidolon.
I can go from an 18 or 20 Charisma if that makes any difference as my biggest ability (it doesnt seem that person physical attributes actually matter anymore) but i would love a little bit of help making him.

Thanks in advance...

[grarrrg]

Is there any type of Eidolon that works better than others?
(or is it simply, they work best in different aspects based upon what i want to achieve?)
Summoner or Sythesist or another?
What is the best type of Eidolon build to go with damage dealing?
I was looking at the Half Elf as a race due to the 1/4 evo points per level... suitable idea?

For Base form, it's either Quad or Biped. Serpentine is only good for niche builds *cough* gundolon *cough*. And Aquatic is only for, well, Aquatic campaigns.
Quad is the only one with access to Pounce.
Biped gets better Reach (Large/Huge).
Either one can serve you well, but take a look at what form-specific evolutions you might want.

For Combat, you can go:
Manufactured, which can get expensive
Natural, which have # of limits on attacks, also recommend you focus on ONE type of attack as Evolutions/Feats usually only apply to ONE type of attack
Both, get Natural attacks up to your limit, then spend points on Arms to hold Weapons.

As for Archetype:
Synthesist is good, but as stated, you gain personal survivability at the cost of Action economy. Also, you CAN cast in Light Armor, have d8HD and 3/4 Bab, and don't NEED as much CHA as other casters, so there is no reason you have to play the "squishy wizard" part.

Since you said Half-Elf, the Wild Caller (http://www.d20pfsrd.com/races/core-races/half-elf/wild-caller-summoner-half-elf) will give you an additional +1/4 Evo per level, at the cost of not being able to take certain evolutions. The only major losses are Energy Immunity (can still take Resist though), Damage Reduction and Weapon Training. The Weapon training is bypassed by just taking a Weapon Prof feat (choose wisely though, you cannot retrain feats).
Also, the Evolutionist (http://www.d20pfsrd.com/classes/base-classes/summoner/archetypes/paizo---summoner-archetypes/evolutionist) is solid, and can combine with the Wild Caller. It mainly gives you a LOT more Non-combat options (min casting time of 1 minute to shuffle evolutions), AND is the only Summoner that can change the Eidolon Base-form (again, mainly 'aquatic').

[CreganTur]

Pounce, claws, extra limbs, claws, rend, improved damage (claws)

That's pretty much the starting point for a high damage build. You pounce and with 4 claw attack attempts you've got a good chance of getting rend off.

Boosting damage on your claws even more, increasing strength, and getting Power Attack are other ways to up your output. You also need good AC. Bump the Nat Armor of the Eidolon as much as you can and don't forget to have your summoner cast Extended Mage Armor to push his defenses even higher.

A little bit of cheese (depending on how you look at it- this is what our summoner did) is take a Small sized race for the Summoner, give him the Mounted Combat feat, and make the Eidolon your mount. Once per round you can make a Ride check with Mounted Combat to completely negate a single attack against the Eidolon.

[Person_Man]

While I agree heartily with the "Summoner is tier 2" and feel that the Summoner's numerical bonuses need to be adjusted, it is possible to make a semi-useless eidolon; a first-time player in my group ended up giving his Eidolon a bunch of minor spellcasting ability (Ray of Frost 1/day! Woo!) and some other mostly useless evolutions and had a rough time for the first level or so. Of course, then he leveled up and got to change all of his evolutions (and I nudged him towards Saph's guide), and his eidolon went from "useless" to "unkillable by anything in his CR and decent damage."

So you are correct. But I would say that even if a player makes the worst possible Eidolon decisions, it's still a meat shield. So a certain number of attacks are going to target it and not you, and it can stand between you and enemies. This is far more effective and useful then most of the defensive and battlefield control abilities possessed by many other "tank" classes.

And then you the Summoner still have spontaneous spells from an good list. So even if you make terrible spellcasting choices in combat, because it's spontaneous, any player will eventually figure out what works and what doesn't through trial and error.

[jaybird]

And then you the Summoner still have spontaneous spells from an good list. So even if you make terrible spellcasting choices in combat, because it's spontaneous, any player will eventually figure out what works and what doesn't through trial and error.

This. At low-mid levels, a Summoner is, at the very least, a Sorcerer with 3+Cha shots of Summon Monster and a much better chance of picking good spells (by virtue of them having a larger ratio of good spells to spells available). That's still pretty amazing.

[Arbane]

I'd suggest taking the Evolution Surge spells, and playing with them as much as possible. That way, you can test evolutions without having to pick them permanently before your next level.

[soulsabre345]

Ok, I'm playing a level 5 summoner in a campaign at the moment, and here's the suggestions I'd give.

Weapon-based Eidolons require a lot of money to keep running, and you need to be able to keep at least 4 or so fairly high-cost weapons to beat out a natural attack based Eidolon, which costs a lot of money and will severely hamper any other item choices.

Natural attack-based eidolons are much cheaper/ easier in that one amulet of mighty fists works for all natural attacks, and costs about the same as 2.5 normal weapons

To the earlier posts mentioning rend, It's worth mentioning rend requires a high strength score to be worth it. Energy attacks is a much better choice if your strength score is lacking, as is shown below.

{table]Attacks|Str needed to surpass 1d6 per attack
1|10
2|16
3|20
4|24
5|28
6|32
[/table]

Also, flight is fairly important, especially since with pounce it can almost entirely remove the need to care about difficult terrain.

So, with all said above, my suggestion for how to spend 10 evo points on a quad Eidolon for high damage follows;
1: Claw
2: Limbs (Arms)
2: Energy Attacks
2: Flight
1: Pounce
1: Claw
1: Whatever

Also, keep in mind that the summoner can carry a small army of wands for various purposes, and that since metamagic is not a great choice on a summoner item creation is a good alternative. You have UMD on your list, and you can add UMD and skilled(UMD) to the eidolon, making you and the Eidolon very capable of using almost any wand very early on. A wand of lesser evolution surge can very much be your best friend if used correctly, and a wand of normal surge can let you heal your Eidolon very efficiently. (use normal surge to grant the Eidolon fast healing 1 for 10 minutes, and you just healed him for 100 hp from a single charge of a 3rd level wand)

[StreamOfTheSky]

I'd do quadruped for pounce, unless you want to attempt to make a "lockdown" eidolon w/ reach and combat reflexes, in which case bidpedal is better. But PF doesn't do lockdown that well. Not till Dazing Assault feat, at least, and that would be level 14 for your eidolon to have BAB +11.

Summoner gets a lot of good spells at reduced levels, including buffs like haste and greater invisibility. They ALSO get a crapton of conjuration (creation) battlefield control spells, such as the create pit line and the fog/cloud spells, and black tentacles.

So while your eidolon pounds in melee, you can do buffing and battlefield control quite well with the summoner himself. It's like having 2 PCs!

For feats, consider the eldritch heritage line, you have the charisma for it. Arcane bloodline gives you a familiar, which you can then take improved familiar for at level 7 to get something that can Use Magic Devices. Now you have 3 characters! :) Oh, and you can take Evolved Familiar feat to give your familiar an evolution, too.
Alternatively...Marid bloodline gets you nothing right away, but at level 11 when you can get Improved Eldritch Heritage, you can get Water's Fury, an at will standard action attack for d6 / 2 levels untyped damage in a line AoE, and save for half damage and to avoid 1d6 rounds of being blind!

For evolutions, you want Pounce (if quad), Str +2, as many extra limbs and claws as you can use along with the bite (if quad, otherwise only take bite on levels where your max # of nat attacks is odd), improved damage, reach (just having it on a single attack will likely give you many more AoOs than you'd have normally gotten), imp. nat armor, Skilled (Perception, UMD...the best skills, basically), and maybe flight. I also love the size increasing evolutions, but if you end up in cramped quarters, you'll end up needing to use Reduce Person on the eidolon a lot.

Wild-caller is a great archetype. Losing Skilled (Use Magic Device, Bluff, and Diplomacy, mainly) and Magical Attacks hurts the most, IMO. At level 10, that's free aligned fang on al the eidolon's weapons for 1 evo point. Losing SM for SNA is a huge downgrade, but you'll mostly have the eidolon out, so that doesn't matter so much.

Eidolon obviously wants combat feats, which ones will depend on how you build it. For any but the bipedal reach weapon user type, Improved Natural Attack (claws) is a surefire great feat choice. Weapon Focus (claws) is good, too.

[StreamOfTheSky]

Since summoner gets spells at reduced levels, I find that metamagic rods work great for them. Try to purchase a bunch of lesser rods, especially Extend, Selective, and Reach. Persistent is nice to use on something like Glitterdust, too. Lesser rods are pretty affordable, too.

[Man With Dog]

So I get the idea here that the Eidolon as a pet (as opposed to Synthesist) is the best way to go?

So far - basing off information from you guys I a guessing a starting block of:
Race: Half Elf (for1/4 evo points per levle giving me another evo point at my level)
Stats:
Cha - Wis - Con - Dex - Int - Str.
Cha being most important - Str being least.

Quadraped (Seems to be favored over biped)
Extra Limbs
Claws
Pounce
Rend
Energy Attacks
Maybe inc Strength?

Feats for Eidolon -
Power Attack
Lunge? or Imp Nat Attack

I am thinking i want to look into geting Large - Flight maybe and possibly look at riding the damned thing at some point (could be fun)


Also - just to state - this is all stolen from a collection of earlier posts and kinda thrown together in a way i will best understand and quick write up once finally decided.

[CreganTur]

Don't forget to look at the new race guide on the SRD- there may be better race options for Summoner now.

[Slipperychicken]

I wouldnt mind idea's that pushed me towards unkillable or a killing machine - or in fact - both would be even better.

I'm pretty sure an Eidolon can use a manufactured weapon and its natural weapons in the same routine. Once you have two points to blow, give your Eidolon arms (ones without Claws. You can't use the same hand for both natural attacks and manufactured in the same round), and maybe MWP: Greatsword/Falchion. Then his Pounce will have all his natural attacks, plus the 2H weapon routine.

You might want to look into the "shadow" evolutions, since they can give your Eidolon Concealment, although at a steep price.

[Barstro]

Feats for Eidolon -
Power Attack
Lunge? or Imp Nat Attack

I am thinking i want to look into geting Large - Flight maybe and possibly look at riding the damned thing at some point (could be fun)


Lunge is a decent idea for a multi-attack pouncer.

No real world experience on my end, but I get the impression that flight is situational enough that it isn't worth the cost of the evolution points; better to cast Evolution Surge when it is needed.

[Morbis Meh]

I'm pretty sure an Eidolon can use a manufactured weapon and its natural weapons in the same routine. Once you have two points to blow, give your Eidolon arms (ones without Claws. You can't use the same hand for both natural attacks and manufactured in the same round), and maybe MWP: Greatsword/Falchion. Then his Pounce will have all his natural attacks, plus the 2H weapon routine.

You might want to look into the "shadow" evolutions, since they can give your Eidolon Concealment, although at a steep price.

The problem with mixing manufactured weapons with natural attacks is that natural attacks become secondary attacks and thus get a -5 until you take multiattack then it's just -2 but why do that when you can simply just go with primary natural attacks and save a feat?

[Deathkeeper]

From experience, flight and manufactured weapons work fine. As does the evolution that increases your range on one weapon-but it's only one, so not as good for a bite/claw/slam kind of thing. My eidolon used a greatsword and did fine, but we were a low optimization party.

[jaybird]

At Summoner 9 you get Multiattack on your Eidolon for free, so if you're going to spend the majority of your campaign at mid-high levels, take a quadruped clawdolon and give it an extra pair of arms as well as MWP for some sort of 2H weapon. Pounce, make your iteratives, then make all your natural attacks at a -2 to hit. It's pretty terrifying.

[grarrrg]

So I get the idea here that the Eidolon as a pet (as opposed to Synthesist) is the best way to go?

So far - basing off information from you guys I a guessing a starting block of:
Race: Half Elf (for1/4 evo points per levle giving me another evo point at my level)
Stats:
Cha - Wis - Con - Dex - Int - Str.
Cha being most important - Str being least.

(the following assumes NOT-Synthesist)
Depending on your exact build, and what you plan on doing, you do NOT need CHA to be your best stat.
What does High CHA get you? More spell slots, better DC's on spells, improves your CHA-skills, and more uses of Summon Monster.

I'll give you the Spell Slots, you may have 'Wizard' level power, but you still only have 'Bard' level slots.
Better DC's? No. The same reason why More Slots is good is the same reason boosting DC's is not worth it. Your spells are of a lower level, so even though you may be casing a "Wizard 7th" it only counts as a 5th for you. That, and most of your spells will be Buffs/Summoning anyway, so DC's don't even matter.
You only get 2 Skills/level, so unless INT is your second best stat, you will NOT be the Social-monkey. It does help UMD though.
Summon Monster is your "Plan B" anyway, and you'll have 5 uses of it with as little as 14 CHA anyway.

So the only reason you "need" CHA is for the Spell Slots anyway.
I'd recommend a more balanced approach, and build your character with an eye towards 'some' combat ability.
Pick your favorite of STR or DEX, add some CON. You don't need a lot of INT or WIS (you're skills will be low anyway, and you have a Good Will save).
DEX is the safer approach (AC/Reflex), and makes Ranged attacks an option.
STR is the more "flank-buddy" approach, that +2 bonus on Flanks goes a long way towards helping your Eidolon land their many-many attacks.
Also remember that you CAN wear Light armor without spell failure.

Your 2 high stats will be CHA and either STR or DEX, followed by CON, then whatever.

[Man With Dog]

Okay - so i had a read through seperate sources and tried to build an Eidolon. Partly by thinking what do i want and mostly by stealing their idea's.

I was torn between two types (which i think i can make one at this level and one at next level (think i change evolutions each level?))

Both are Base Quadrapeds.
I am a Half Elf - so 9 evolutions plus 1 for Race at level 4.
It is labelled as one designed for one big attack - sounded cool enough.

Bite(given as starter) Bite(for additional dmg), Imp Dmg (Bite), Reach (Bite), Ability Inc (Str), Trip (Bite) Poison (Bite)
Think that is 9 evolutions?

Alternatively or more so in a few levels time.
Claws, Pounce, Rake, Remd, Energy Att, Limbs (Arms)
Is all i can get at current Level
Next Few levels:
Claws (Arms), Ability Increase (Str), Imp Dmg.

Both Eidoons would get Power Attack, Imp Nat Attack and Lunge as feats.

If these are okay - please say.
If they are not okay - please say.

If you can build better for my level - I would love to hear even more.

[Bomaz]

Extra evolution feat in ultimate magic, +1 ep

[Man With Dog]

Extra evolution feat in ultimate magic, +1 ep

Thats not a build...
Is it?:smallconfused:

[grarrrg]

change evolutions each level?

Yes, you can completely change around your Evolution each level (or whenever you want with the Transmogrify (http://www.d20pfsrd.com/magic/all-spells/t/transmogrify) spell).
And you are stuck with your chosen base form (except for the Evolutionist (http://www.d20pfsrd.com/classes/base-classes/summoner/archetypes/paizo---summoner-archetypes/evolutionist) archetype which can change it at level up).
But keep in mind that you can NOT change Feats EVER. Once you choose a Feat you are stuck with it. So choose VERY carefully.
Your Eidolons Ability Increases are also permanent, but so long as you stick to STR/DEX/CON (and pay attention to when your natural +STR/DEX happens) you'll be fine. Tip: 1st one goes into CON.



I am a Half Elf - so 9 evolutions plus 1 for Race at level 4.
Level 4 has 7 base Evo-points. +1 for Half-Elf is 8. If you take the Extra Evolution feat that'd be 9 total.

The Wild Caller (http://www.d20pfsrd.com/races/core-races/half-elf/wild-caller-summoner-half-elf) archetype can add another +1, but you lose access to certain Evolutions. The only "good" ones you lose are Magic Attacks (which is 'meh' once you get the Natural Attack-necklace), Energy attacks (not a total loss), Energy Immunity (this one hurts, but you still have Resistance), and Damage Reduction (no quick fix).

Also, since you are going straight Summoner, trade your Multitalented (http://www.d20pfsrd.com/races/core-races/half-elf) Racial trait for something else. Either Arcane Training, or Dual-Minded. I'd recommend Dual-Minded and then dump WIS.


Bite(given as starter) Bite(for additional dmg), Imp Dmg (Bite), Reach (Bite), Ability Inc (Str), Trip (Bite) Poison (Bite)
Think that is 9 evolutions?
You can't take Poison until level 7. I'd also skip Imp Dmg (Bite) for now, as you're only getting a +1 damage return.
Throw on a pair of Claws, you have 4 Nat Attacks, may as well try to use them. Imp Natural Armor is always good, as is Pounce with the 2 Claws.


Alternatively or more so in a few levels time.
Claws, Pounce, Rake, Rend, Energy Att, Limbs (Arms)
Is all i can get at current Level
Next Few levels:
Claws (Arms), Ability Increase (Str), Imp Dmg.
Rend is not available until level 6. And unless you plan on using a Weapon, it doesn't pay to give it Arms (yet), as you can just put the Claws on your Feet.


Both Eidoons would get Power Attack, Imp Nat Attack and Lunge as feats.

Back to the "Feats are permanent" thing.
Imp Natural Attack makes you choose 1-type of attack. So if you pick Bite, you are stuck with better Bite damage FOREVER. That's fine if you plan on making full use of your Bite attack. Not so much if you plan on shifting towards Claws later on.

[Barstro]

Throw on a pair of Claws, you have 4 Nat Attacks, may as well try to use them.



I disagree with grarrrg on this point if you are making a bite/trip eidolon. I suggest foregoing extra attacks to concentrate and enhance the bite attack (maybe reach). This is especially true once you get to level 9, where having only one attack with multi-attack gives you even more tripping chances.

Again, that is ONLY if you are going for bite/trip. If you have any other strategy, I'd go for the extra attacks as grarrrg suggests (and probably get rid of Trip). But this all depends on the makeup of your party. You do have several levels to test different builds.

[Man With Dog]

I could quite easily go with Synthesist.

But nobody seems to think they can match up to the Eidolon + Sythesist set up. Or at least nobody came up with any idea's

[Barstro]

But nobody seems to think they can match up to the Eidolon + Sythesist set up. Or at least nobody came up with any idea's

The problem is;
1) Eidolon + Summoner gets "extra" actions compared to Synthesist
2) If asleep/unconscious; a Synthesist is now without armor, in the middle of melee, while a standard Summoner is generally outside of melee and a little safer.
3) Synthesist relies a lot more on discussing things with the DM first to determine how to handle gray areas. There is (to my knowledge) no ruling on what happens when someone else casts Enlarge Person on a fused Synthesist.

Synthesist can be a great niche class. But it's best to discuss it with your DM first to make sure that you will be allowed to do whatever tricks you have planned.

[grarrrg]

I disagree with grarrrg on this point if you are making a bite/trip eidolon. I suggest foregoing extra attacks to concentrate and enhance the bite attack (maybe reach). This is especially true once you get to level 9, where having only one attack with multi-attack gives you even more tripping chances.

He already has just about everything he can Bite+Trip wise. But one of his Evolutions was invalid for the listed level (Poison), so he has extra points.
And he's only level 4, so level 9 is a LONG way off, plenty of time to readjust Evolution points.


There is (to my knowledge) no ruling on what happens when someone else casts Enlarge Person on a fused Synthesist.
:smallconfused:
He becomes 1 size bigger.
Like normal.
The Eidolon is already a valid target for Enlarge Person, and the Synthesist is "inside" the Eidolon, so as long as the Eidolon is at least the same size as the Synthesist there is no problem.

REDUCE Person on the other hand...

[Barstro]

:smallconfused:
He becomes 1 size bigger.
Like normal.
The Eidolon is already a valid target for Enlarge Person, and the Synthesist is "inside" the Eidolon, so as long as the Eidolon is at least the same size as the Synthesist there is no problem.

REDUCE Person on the other hand...

I agree that the Synthesist doing the casting causes both himself and the eidolon suit to change sizes, it is not as clear if anybody else casts it on them.

The unfused Synthesist is a valid target. The fused Synthesist might not be; since it is treated as outsider (not valid target) or humanoid (valid target) whichever is worse.

Again, I don't keep up on errata, so your explanation might be RAW now.

[grarrrg]

I agree that the Synthesist doing the casting causes both himself and the eidolon suit to change sizes, it is not as clear if anybody else casts it on them.

The unfused Synthesist is a valid target. The fused Synthesist might not be; since it is treated as outsider (not valid target) or humanoid (valid target) whichever is worse.

Again, I don't keep up on errata, so your explanation might be RAW now.

I see now, the key part is "someone else" not "enlarge person".
In that case I would say only YOU (Synthesist) can Enlarge you. Reason being that you-the-not-eidolon kind of ceases to physically exist while the Eidolon-Suit is summoned. Leaving only the Eidolon as a valid physical target.
If it was a "mental" spell, then you are the only valid target regardless.

[StreamOfTheSky]

Also, since you are going straight Summoner, trade your Multitalented (http://www.d20pfsrd.com/races/core-races/half-elf) Racial trait for something else. Either Arcane Training, or Dual-Minded. I'd recommend Dual-Minded and then dump WIS.

Dual Minded replaces adaptability. The only option that only replaces multitalented is Arcane Training, which...will let you use scrolls/wands/staves of spells on the summoner list as if you were +1 CL (so, very minor staff boon, basically worthless for the other 2). It's a pretty terrible ability, but sadly the only swap you can make. Pretty much everything else costs Adaptibility, the Half-Elf variant options are really poorly done...

[grarrrg]

Dual Minded replaces adaptability. The only option that only replaces multitalented is Arcane Training, which...will let you use scrolls/wands/staves of spells on the summoner list as if you were +1 CL (so, very minor staff boon, basically worthless for the other 2). It's a pretty terrible ability, but sadly the only swap you can make. Pretty much everything else costs Adaptibility, the Half-Elf variant options are really poorly done...

Well blah.
Still, Arcane Training is still better than an otherwise worthless Multitalented.
Or if he doesn't want Adaptability either that still opens up options.