I don't have the reflexes to be that great at most action games, but two RPGs spring to mind.
The first is Bravely Default. Now I'm not in any sort of community of players, but I wouldn't be surprised if there wasn't that many people who know as much about this game as I do. With over four hundred hours in it I know the game mechanics like the back of my hand, and I can bring down a superboss in 5 turns, except for Turtle Dove?, which requires a unique setup by virtue of its capped defense. Anything else only needs a couple turns of buffs to tear apart. Most of the high end strategies I've seen from other people involve using Stillness and speed control to deal damage while preventing yourself from taking any, but these sets are inevitably weak to status and any bosses, such as Lucifer, that can change their speed stat. I use two different setups, based on the same class set.
Ninja @ Dark Arts
Ama-no-Marakumo
Ama-no-Marakumo
Royal Crown
Brave Suit
Hyper Bracers
Sword Magic Amp
Drain Attack Up
Hawkeye
Precision
This is, to my extensive knowledge, the most reliable way to deal 20K damage in a single attack. By using the Drain Sword Magic (cast from the Blood Blade item), combined with those support abilities, and then using Life or Death (while Fairy Ward is up so you aren't Doomed, of course), allows you to hit enough damage per hit to deal cap damage with each hit of the two-hit attack, although a couple bosses require you to lower their def first too. Then Braving four times lets you deal 80K in one turn, on one character. I run two different setups focused around this build--the first uses only one of these, along with a Freelancer @ Singing, a Vampire @ Medicine, and a Ninja @ Spiritism. Using Stillness to safely set buffs, with Giant's Draft to live powerful hits, and Mimic Hero to keep up Braving four times per turn. The other setup varies a little more, but is three ninja with different secondary abilities so they can buff each other themselves, and a Mimic Hero to fuel their Brave. The second has a lot less defense and is thus riskier, but tears apart anything in just a few turns, dealing about 240K per turn.
...Yes, I put way too much thought into optimizing for a game that doesn't require optimization to beat.
The other is Transistor. I could go really in-depth on my setup and all that, but I think I'll just leave
this here instead.