Advice for arcane trickster

[Ryswinn]

Hello, my DM has created a campaign and he decided part of our background. He told me that I'm going to play an investigator who works with "police" and suggested me choosing a magic class. I'd like to go for an arcane trickster because I don't wanna play a full caster.
My stats are: 18 DEX 16 CON? 12 INT? 12 WIS 11 CHA10 STR.
I can't decide if it's better 16 CON and 12 INT and make a forest gnome or a human variant and take 16 INT and 14 CON (+1 racial traits and Resilient). I'm also considering the idea of playing an high elf and using the longbow instead of going melee.

[RogueJK]

or a human variant and take 16 INT and 14 CON (+1 racial traits and Resilient)

That would certainly be a more optimal spread, if you want to be able to utilize your casting to the fullest. Start 18 DEX, 16+1 INT, 12+1+1 (Res) CON. I'd then go 20 DEX at 4th and 18 INT at 8th with Fey Touched (or vice-versa at 4th/8th if you want the extra spells sooner), and then 20 INT at 10th.

ATs can get by with a 12/14 INT if they have to by sticking to purely Utility/Buff spells, but doing so removes a chunk of your otherwise good spell options that rely on enemy saves and require a decent INT in order to stick. Suggestion in particular is a great AT spell, handy both in and out of combat, that wouldn't be usable with a low INT.

As for melee vs. ranged, ATs can get a lot of mileage from Booming Blade (Action) + Cunning Action Disengage (Bonus Action), and that's going to be your best option for optimized damage output, especially if combined with using your Concentration for Shadow Blade. But that requires melee. A ranged AT focused on using a Longbow is doable, but will be a little further behind the curve in damage output, and going High Elf will require accepting a lower INT.

So I'd stick with a Rapier (or Shadow Blade) in melee with Booming Blade as your primary option, and have a Shortbow or Light Crossbow in reserve for times when ranged attacks are needed.

[Falconcry]

Ranged vs melee doesn’t need to be an either or decision. Build for both. Elven accuracy/ sharpshooter with ba hide works great and a booming blade /shadow blade on standby if they close the distance is a nice surprise. Well not so much for them.

[Verble]

Con is nice but I'd go with the higher intelligence. This increases your save DC's for spells and helps your arcana score that is used for disarming magical traps.

For my AT I took a 2 level dip in warlock(GOO reflavored to be Baba Yaga) and found that Invocations helpful for at will casting, disguise self and detect magic on a whim is very useful.
Though it seems you may not have the Cha for it.

[quindraco]

Hello, my DM has created a campaign and he decided part of our background. He told me that I'm going to play an investigator who works with "police" and suggested me choosing a magic class. I'd like to go for an arcane trickster because I don't wanna play a full caster.
My stats are: 18 DEX 16 CON? 12 INT? 12 WIS 11 CHA10 STR.
I can't decide if it's better 16 CON and 12 INT and make a forest gnome or a human variant and take 16 INT and 14 CON (+1 racial traits and Resilient). I'm also considering the idea of playing an high elf and using the longbow instead of going melee.

I'm playing an arcane trickster right now! I'm an eladrin, not a high elf, and I highly recommend it - misty step is for winners, and I don't really feel like I'm desperate for another cantrip.

Some tips:

If you're using Tasha's, heavy crossbow > longbow for rogues, every time.
Elves rule, variant humans drool. No, really. Elves can take the elven accuracy feat, absolutely clutch on a rogue - and variant humans are Tasha's custom lineage but worse. I recommend focusing on races with excellent mobility (I went for teleport, but flight is also excellent), excellent stats (half-elves and mountain dwarves, basically), or other specific racials super awesome on a rogue (kobolds). Humans don't even have darkvision.
You don't need any INT on an Arcane Rogue unless you choose to - mine is INT 10. The trick is avoiding enchantment spells (which inflict saves, and hence care about your INT, but since you also care about DEX for doing rogue stuff and CON for living and maintaining concentration, it's unlikely you'll be able to maintain a competitively high INT at higher levels). My starting statline was DEX 17 CON 16 WIS 14 INT 10 CHA 8 STR 8 (I specifically wanted to avoid stepping on my party face's toes, which is why I dumped charisma). I'm loaded up with illusion spells and a pet owl (you absolutely do want Find Familiar).
If you're gonna gnome, check out deep gnomes. They're super neat.

[5eNeedsDarksun]

I'm DMing an AT at the moment, and they are definitely rare birds in a sense. You have access to blade cantrips and a reliable way of creating advantage (find familiar) with a single attack. So unlike most rogues it seems like you are taylor made to use a single melee attack. This allows you to use ASIs for Dex, as there is no need to spend them on feats like XBE for a 2nd range attack.
The character I'm DMing is a winged tiefling, so I can say that works, though I'd agree with the poster who mentioned elves and elven accuracy. You'd get that 3rd dice on your one attack to make sure you don't miss and you can still (assuming point buy) get to Dex 18 by 4th level.
Also, check out how Sentinel interacts with Mirror Image for your 8th or 10th level ASI.

[Ryswinn]

Thank you all for your advice!

[Jon talks a lot]

I'm DMing an AT at the moment, and they are definitely rare birds in a sense. You have access to blade cantrips and a reliable way of creating advantage (find familiar) with a single attack. So unlike most rogues it seems like you are taylor made to use a single melee attack. This allows you to use ASIs for Dex, as there is no need to spend them on feats like XBE for a 2nd range attack.
The character I'm DMing is a winged tiefling, so I can say that works, though I'd agree with the poster who mentioned elves and elven accuracy. You'd get that 3rd dice on your one attack to make sure you don't miss and you can still (assuming point buy) get to Dex 18 by 4th level.
Also, check out how Sentinel interacts with Mirror Image for your 8th or 10th level ASI.

I decided to build this, and it seems really powerful.

Race: Shadar-Kai
Class: Rogue 20
Subclass: Arcane Trickster
Ability Scores: 8 STR, 15+2 DEX, 14 CON, 15+1 INT, 8 WIS, 10 CHA
ASI’s: Elven Accuracy (DEX) @4, +2 DEX @8, Sentinel @10, War Caster @12, Mobile @16, Alert @19.
Equipment: Studded Leather. DEX-based Melee Weapon.
Background: Orzhov Representative

Spells Known:
Cantrips: Green-Flame Blade, Mage Hand, Guidance, Prestidigitation
1st Level: Find Familiar, Sleep, Disguise Self, Tasha’s Hideous Laughter
2nd Level: Mirror Image, Misty Step, Hold Person, Shadow Blade
3rd Level: Hypnotic Pattern, Spirit Guardians, Motivational Speech, Phantom Steed
4th Level: Greater Invisibility, Dimension Door

For Hordes: Cast Spirit Guardians, use the dodge action.
For One Target: Pre-cast Find Familiar. Turn 1, cast Mirror Image. Turn 2+, Action Cast Green-Flame Blade with triple advantage (Familiar using the help action) for 1d8(Scimitar)+5(DEX Mod)+3d8(Green-Flame Blade)+10d6(Sneak Attack). Another way to gain advantage on your attacks is to precast mage hand, then use versatile trickster. The third way is to use shadow blade. If the target attacks you and hits your mirror image, then you get a sentinel attack, meaning that you have a really good chance to get an OA from the three separate ways you have to get one.

I like this version a lot because it has the versatility to switch between stomping hordes and doing a lot of damage with no resources required. It's a really good consistent damage dealer, similar to zealot barbarian in a way. At the same time, Out of Combat utility is pretty dang good. We have guidance, spells like disguise self and Greater Invisibility, all the standard rogue things, and Mage Hand Legerdemain.

[Ryswinn]

I think I'll play a human variant with +1 int, +1 cha and Fey touched so I'll have: 18 dex, 16 con, 14 int, 12 cha, 12 wis and 10 str. Then I'll multiclass into 1 level fighter and take defense for fighting style, so my AC will be 16.

[RogueJK]

Your AC should easily be 16 even without Defense Fighting Style. 12 from Studded Leather and +4 from 18 DEX = 16 AC.

Defense would then bump it to 17.

Then also using a Shield from Fighter armor proficiencies could raise it to 19, but would put a cramp on some of your spellcasting if your DM is a strict adherent to "must have a free hand to cast spells with Somatic/Material components". It'd still be usable with Booming Blade specifically, though.

[quindraco]

I decided to build this, and it seems really powerful.

Race: Shadar-Kai
Class: Rogue 20
Subclass: Arcane Trickster
Ability Scores: 8 STR, 15+2 DEX, 14 CON, 15+1 INT, 8 WIS, 10 CHA
ASI’s: Elven Accuracy (DEX) @4, +2 DEX @8, Sentinel @10, Medium Armor Master @12, Warcaster @16, Alert @19.
Equipment: Studded Leather until Level 12, then Half-plate. DEX based Melee Weapon.
Background: Orzhov Representative

Spells Known:
Cantrips: Green-Flame Blade, Mage Hand, Guidance, Prestidigitation
1st Level: Find Familiar, Sleep, Disguise Self, Tasha’s Hideous Laughter
2nd Level: Mirror Image, Misty Step, Hold Person, Shadow Blade
3rd Level: Hypnotic Pattern, Spirit Guardians, Motivational Speech, Phantom Steed
4th Level: Greater Invisibility, Dimension Door

For Hordes: Cast Spirit Guardians, use the dodge action.
For One Target: Pre-cast Find Familiar. Turn 1, cast Mirror Image. Turn 2+, Action Cast Green-Flame Blade with triple advantage (Familiar using the help action) for 1d8(Scimitar)+5(DEX Mod)+3d8(Green-Flame Blade)+10d6(Sneak Attack). Another way to gain advantage on your attacks is to precast mage hand, then use versatile trickster. If the target attacks you and hits your mirror image, then you get a sentinel attack, meaning that you have a really good chance to get an OA from the three separate ways you have to get one.

I like this version a lot because it has the versatility to switch between stomping hordes and doing a lot of damage with no resources required. It's a really good consistent damage dealer, similar to zealot barbarian in a way. At the same time, Out of Combat utility is pretty dang good. We have guidance, spells like disguise self and Greater Invisibility, all the standard rogue things, and Mage Hand Legerdemain.

Booming Blade is the mono-target one. Green-Flame Blade does less damage to one target and more damage to two. Without a GM ruling overriding the RAW, you cannot combine Booming Blade or Green-Flame Blade with Shadow Blade. I've never played with the overpowered Ravnica backgrounds, but I'm an AT, and I can tell you Phantom Steed is a waste of a spell slot on you. And the Medium Armor proficiency is a waste of a feat.

[Jon talks a lot]

Booming Blade is the mono-target one. Green-Flame Blade does less damage to one target and more damage to two. Without a GM ruling overriding the RAW, you cannot combine Booming Blade or Green-Flame Blade with Shadow Blade. I've never played with the overpowered Ravnica backgrounds, but I'm an AT, and I can tell you Phantom Steed is a waste of a spell slot on you. And the Medium Armor proficiency is a waste of a feat.

Sure, Green Flame Blade does 3d8 to one target and 3d8+Spellcasting mod to the second target. I like it more though because that +3 damage isn't too relevant and Booming blade requires movement, meaning enemies can just negate the damage.

Correct on Phantom Steed.

Correct on Shadow Blade. However, that is not the point of Shadow Blade for me. It is to give me advantage on attacks if my familiar dies. Sneak attack is more damage than the blade cantrips

Medium Armor Proficiency? I already get that as a rogue. Do you not know what Medium Armor Master is?

[RogueJK]

Medium Armor Proficiency? I already get that as a rogue. Do you not know what Medium Armor Master is?

No, Rogues only get Light Armor proficiency. A straight-classed Rogue would have to spend a feat on Moderately Armored to get Medium Armor (and Shield) proficiency, and only then would be able to spend a second feat on Medium Armor Master.

Or you'd need to be a Mountain Dwarf or Githyanki and have racial Medium Armor proficiency, which would allow you to jump straight to spending a feat on Medium Armor Master. Or dip a level in Fighter/Cleric/Paladin/Ranger to get Medium Armor proficiency.

[Jon talks a lot]

No, Rogues only get Light Armor proficiency. A straight-classed Rogue would have to spend a feat on Moderately Armored to get Medium Armor (and Shield) proficiency, and only then would be able to spend a second feat on Medium Armor Master.

Or you'd need to be a Mountain Dwarf or Githyanki and have racial Medium Armor proficiency, which would allow you to jump straight to spending a feat on Medium Armor Master. Or dip a level in Fighter/Cleric/Paladin/Ranger to get Medium Armor proficiency.

Oh crap, I could have sworn they had medium armor proficiency. Thank you.