Dilemma: Maxing a Primary Ability Score or Choosing a Feat (or Feats)

[Expected]

I'm going to be playing a Wood Elf Arcane Trickster and using point-buy, I will start with 17 Dex (18 at level 4 when I take Elven Accuracy), 15 Con, and 16 Wis. The dilemma is that I can choose to max Dex at levels 8, 10, 12, or 16 (19 at the latest), or take a feat among Resilient (Con), Sentinel (I will be using Mirror Image and be in melee with rapier and shield because of a 1-level dip in Fighter), Lucky, Mobile, and/or War Caster (ABSOLUTELY needed when I get 3rd-level spells for Haste).

The additional +1 modifier to Dex grants me +1 attack, +1 damage, +1 to Dex skills and saving throws, but a feat, like Resilient (Con), allows me to get 16 Con and a +3 Modifier. Should I max Dex early or wait until later and get a feat or feats? Any advice or criticism is appreciated--I want to optimize this character at every level.

[Corran]

If your intention is to stay in melee reach of the enemies and not to hit and run, then I think blur will serve you better than mirror image. It will last longer for sure, and since I don't see any other good contenders for concentration (not to mention the fact that you don't want to spend two turns casting a spell and missing on sneak attack, ie casting mirror image and then casting a concentration spell is a stretch action economy-wise), I would say that blur is the better choice. Personally I would avoid both spells, unless I was making a sentinel build, in which case I would aim for blur rather than mirror image, for the aforementioned reasons.

As far as saving throws go, and given that you plan to involve fighter levels, I would prioritize con and wis saves (as slippery mind comes too late, even later with multiclassing). So I'd start fighrer for con saves, and take resilient for wis saves. A good dex score and evasion is enough to take care your dex saves against damaging effects that target dex. You might not be perfectly equipped against effects that target dex saves and instead of damage restrict movement, though I think such effects are not all that common (web and one of the beholder rays are the first that come to mind, after a recent post I read regarding this topic), or at least, they are far less in number than effects that target wis and con saves respectively.

Throwing sentinel on top of a rogue is very dangerous in my mind, but planning carefully a mc AT rogue/ BM fighter build (split of 14/6 or 13/7) is the best/safest way to do this IMO. I could go into more detail on that, though since I am not sure if this is something you are interested in, I will stop here instead.

[Keravath]

I think the idea behind mirror image is that when he is attacked and the attack goes to one of the images instead, he can then use sentinel to obtain a reaction sneak attack against the opponent that tried to hit him.

The relevant text is:

Sentinel:
"When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn't have this feat), you can use your reaction to make a melee weapon attack against the attacking creature."

Mirror Image:
"Each time a creature targets you with an attack during the spell's duration, roll a d20 to determine whether the attack instead targets one of your duplicates."

The key here is that both abilities state "target". Sentinel says a target other than you and mirror image image has the effect of forcing the attack to "target" one of the duplicates. As a result, when the attacker tries to attack you ... ends up targeted on a duplicate (which is clearly not YOU) ... you can trigger sentinel on that attack and execute a reaction sneak attack against the attacker.

P.S. Mirror Image doesn't require concentration so it will stack with haste when he gets it at higher levels.

[Keravath]

I'm not sure why you will absolutely need warcaster when you want to cast haste. Haste will take your action on the first round of combat ... so you just cast haste and draw your weapon as a free action.

Warcaster is only needed when you want to cast a spell with weapon and shield in hand ... this is necessary for characters that don't want to juggle or drop weapons during combat to free up a hand and most particularly if you want to cast the shield spell as a reaction.

So I'm not sure where the "absolute" need for warcaster comes from in your case except perhaps if you don't want to sheathe your weapon if you have to recast haste during combat.

[Expected]

So I'm not sure where the "absolute" need for warcaster comes from in your case except perhaps if you don't want to sheathe your weapon if you have to recast haste during combat.

I intend to cast Haste once I get 3rd-level spells and since I'll be in the frontlines, I will be an attractive target (hence the fighter dip for shield proficiency and Fighting Style (Defense)). Haste states, "When the spell ends, the target can't move or take actions until the end of its next turn." So if I am attacked (which I most likely will be the main target unless there's a threatening tank) and lose concentration, I also lose a turn, which is the logic behind taking Resilient (Con) and War Caster and having high Con. Also, I will have the option of casting spells without sheathing my weapon or dropping it. Now at later levels, I can ask a caster ally to cast Haste on me and I can cast something else such as Greater Invisibility (which synchronizes REALLY well with Sentinel). If I don't need War Caster, I would gladly replace it with something else like Mobile or Lucky.

[Expected]

Throwing sentinel on top of a rogue is very dangerous in my mind, but planning carefully a mc AT rogue/ BM fighter build (split of 14/6 or 13/7) is the best/safest way to do this IMO. I could go into more detail on that, though since I am not sure if this is something you are interested in, I will stop here instead.

I'm completely open to advice and criticism--if you think it'd be better, I'd love to hear it. The whole point of this thread is to use feedback to improve on the build I had in mind.

[Laserlight]

"Optimize" for what? I prefer to optimize to "be more interesting", so I tend to take feats that let me do more things.

[Expected]

An important combo that I forgot to mention is Mirror Image (or an ally that is attacked) + Sentinel + War Caster + Booming Blade for off-turn Booming Blade Sneak Attacks and it is even better if it crits which has a higher probability thanks to Elven Accuracy. However, I would need advantage for Elven Accuracy to work so Greater Invisibility or another method to gain advantage.

[Expected]

"Optimize" for what? I prefer to optimize to "be more interesting", so I tend to take feats that let me do more things.

Which is exactly what Sentinel does--I'd get to Sneak Attack more than once a turn. If that's not good enough, I could select Mobile and Booming Blade + SA and disengage. There's also Lucky which can turn disadvantage into tri-vantage.

As you can tell, I'm primarily concerned with combat optimization. However, I am an optimizer and not a munchkin, so roleplay is just as important. My character's backstory and skill proficiencies will help me to roleplay during times without combat.

[Laserlight]

Which is exactly what Sentinel does--I'd get to Sneak Attack more than once a turn. If that's not good enough, I could select Mobile and Booming Blade + SA and disengage. There's also Lucky which can turn disadvantage into tri-vantage.

I love BB but I've found a lot of monsters either have someone else adjacent or can attack from range. I wouldn't pick Mobile just in the hope of doing more BB damage.

[Expected]

True. Especially if it is a melee enemy (in that case, the tank is probably right next to them). I'd be relying on them to still target me as opposed to the tank, and if so, they receive the additional damage. If not, Sentinel activates should I still be standing near the enemy.

I will have good AC because of high Dex + light armor, a shield, and Fighting Style (Defense) so I won't be too worried about taking too much damage. And because of my high DPR, the enemy would be a fool to ignore me. I could just move to a ranged enemy with Find Familiar (Owl) or the AT bonus action that grants advantage, that way I essentially guarantee a SA and Sentinel when they shoot at me or someone else. All of this is assuming that the situations go as planned (which rarely is the case).

[Keravath]

"Good" AC is often not good enough :)

Light armor + dex + shield + defence = AC20 without magic items.

By the time you hit level 8 to 10, your opponents could have +7 to +12 attack modifiers with 2 to 4 attacks (3 attacks is pretty common). These will hit on an 8 to 13 or likely 1/2 the time.

Basically, if you are in melee range, you will get hit sometimes unless you have Mirror Image or other spells running. So .. you should keep that in mind. The odds of maintaining a concentration spell are probably not that great.