Advice for letting "power-gamers" feel powerful?

100 dmg is what top lvl characters max out towards (without crazy items) say simple stuff like power word kill, or a fighter doing 2d6, 4x and then action surges, tac on STR bonus and you can hit 100.

But fireball, at 5th lvl maxes out at (8d6)48, higher spells. Sure you can upcast, but getting 100 dmg takes at least 10th lvl i would wager, without crazy magic items. Physical atk is even harder than spells.

Mages are glass cannons, so if all he wants is firepower he can go that route. But gotta lower expectations.

Ill assume he meant 100 possible damage. Which is insane.

Honestly its not going to be easy. Making a power gamer feel challenged means hurting the other guys cause the combats need to be harder unless you specifically challenge his other abilities in non combat encoutners.

Honestly I don't like power gamers myself. I dont find that kind of play style fun, on either side of the table.

I'm going to be honest with you, being upfront about your goals for the game and expectations for players is 100% part of being a good DM (regardless of anything else). Even if, this is the exception not the rule, you were to just say "I'm not telling you anything about the setting, what to expect, or what you'll be playing, my goal is to surprise the hell out of you." That is still doing what I propose.

That said. My goal is to tell good stories and I expect players to help me do that by participating in those stories and help mold and craft the stories as active participants. Aside from that, I'm pretty open to suggestion.

Players who want to minmax, optimize, and focus on numbers over words can play a video game. I don't run my game(s) for that purpose. If this were me, I would explain the goals and expectations of my game, his desires aside. If he wants to play with the acknowledgement that this is going to be the game being run and these are where its headed, then he can do whatever he wants with this character.

Note 1: I'm not against players optimizing, but it shouldn't be the focus in my games. That said, if you are down from running combat-simulation D&D games all power to you. I know people who play and love those games.

Note 2: From a balance standpoint, the only way I would let a mystic in my game was if everyone was playing a mystic (or openly knew they are going to be sub-optimal if they played a non mystic, like a character playing a non-Jedi in a SWRPG game). Maybe they would be broken, but they'd all be broken together.

Offer the character something powerful to fight alone. Seriously, have the rest of the party engaged with other enemies (perhaps even a group of the same kind of creature) but give his optimized build a chance to shine or fail dramatically without intervention from anyone else. Have that fight matter just as much as the rest. If his build and dice fail, then make the loss hurt him more than the rest of the party.

So other people have covered the mechanics of having to do 100 dmg so I'll go into how to deal with it if/when he gets there. This is him wanting to do a cool mechanical thing which is just as valid as wanting to do a cool roleplay thing. And as much as you should shy away from video game logic in roleplay with mechanics it can be very useful.

So obviously you can just add hp to enemies/add enemies to an encounter to slow the encounter down if he is dealing more damage than you thought. You could have temporary buffs (wizard steps in a arcane fountain just before a boss fight and adds x damage to y). Enemies could be weak to his main damage type (perhaps give the players a chance to poison the enemies to achieve this). Have the boss go into a defensive stance in the fight and need a large burst of damage to break the stance or maybe there is a defensive pylon/generator thing nearby that needs to be bursted down to lower defenses.

These are just example to make him feel more powerful and (if he optimizes enough that its causing you some issues) lets you funnel that excessive damage away from the boss but still feel important. Remember HP vs HP combat is the most defined aspect of dnd. It is honestly the easiest optimization to deal with so don't jump straight to nerfing him if he is doing more damage than you thought; try and get creative.

Have a real tough boss thats vulnerable to Psychic damage.

He'll only have to do 50 damage to do his 100 damage now. If he rolls well on an upcasted Lethal Strike it should be good enough.

I think it's a fair compromise.

FWIW, I think I DM with some 7s and 8s as well as a closet 9 on the Powergaming Scale and honestly, character agency is way bigger to make these guys feel good.

In terms of challenges, I tend to place obstacles between the characters and their objectives in terms of something that should jog their creative brain (eg: terrain, choosing one target among many, timed objectives), because that's the challenge you provide, as the damage that they deal is a reward in itself for them.

Source: Had a level 7 Paladin do 123 damage in total in a GWM Critical Hit with a Level 2 smite against a custom huge skeleton monster that looked like a basilisk with swallowing abilities and burrowing (while melding) with the pit of bones that the area they were fighting on that had 280hp but vulnerability to bludgeoning.

The Paladin and another fellow Paladin (Level 6) faced the skeleton beast while other party members were trying to kill the wizard who summoned it on higher ground as well as a wall of force protecting it.

Everyone was pretty fucking estatic about that critical hit as the situation was pretty fucking dire as the chamber behind the summoner wizard was undergoing another ritual.

I've had success in the past by feeding my power-gamer overblown descriptions and special effects.

He wasn't really looking to "beat the system" though. He just wanted to be a badass... so I tailored my combat descriptions to make him sound like one.