Vaporstrike

The super special final boss power-up where you get a new transformation or some sort of limitation is removed to make it as exciting as possible. Gives me life.

Double jumps. I don't care how little sense they make, give me double jumps. They're never not fun.

And this is a bit more of a feeling than a mechanic or anything, but anytime I think "Wait, would this crazy idea actually work?" and the game says yes; that's the mark of a good-ass game.
Think of it as the opposite of the insurmountable kneehigh fence, where you feel like something should be possible but it's not.

• Breath of the Wild and Tears of the Kingdom were both great for it ("Wait, could I just make ice stairs up that waterfall?" - Yes.), but it shows up more and more lately.
• Baldur's Gate 3 had it ("Wait, can I just lie to the Goblins to lure them into a trap?" - Yes.)
• Baba is You was amazing ("Wait, if I make 'Baba is You' and 'Baba is Win', don't I just win automatically?" - Yes.)
• Roguelikes tend to have it ("Wait, if all Hearts count as Diamonds and every Diamond gives me +4 multiplier, won't I be able to play a huge flush basically every hand?" - Yes.)
• RPGs with a lot of options to build your character do it, especially those with Job systems.

And so on and so forth.

When you eventually unlock some insane mobility ability later in the game to let you zip through areas - especially if you can retread early areas. Great power trip. The Kingdom Hearts 2 super glide comes to mind.

Not a gameplay feature, but the aesthetic of 2D sprites on a 3D background always feels so damn comfy to me.

Using my own imagination!

Example: Octopath had some people whining about how the characters "just joined" without any good interaction. They didn't need to have 2 hours of dialogue. Fill in the rests as you wish.

Same goes, and using the same example, Octopath, is when the fuck to they take shit or a piss?

All can be imagined if you want to.

The ability to manually put away your weapon, especially if it is stylish.

Nioh is probably the best example I can think of off the top of my head. It feels great to pull off some bad-assery and then sheath your sword as the enemy dies. It's completely unnecessary (there's no difference to your character whether your weapons are sheathed or not), but its sort of like a punctuation mark to combat, like a declaration of victory.

There is so many, one I can think right now is when they respect save files in many ways. Giving you space to save, from a lot of slots to "as long as there's space on your hard disk", leave notes, marking it with colors (FF7, indirectly) etc etc I'm a maniac with these things.

My all time favorite gaming moment, no contest, is when they provide you with a sudden permanent power bump and the rules or the power dynamics change.

Spoilers for Skies of Arcadia:

That moment for me was when you get the Delphinus in Skies of Arcadia. I knew you get your own ship in that game, but I had no idea it would be one of the enemy's own, latest, baddest-ass battleship. It actually stunned me and to some extent I've been chasing that videogame high ever since. Man, what a memory.

When you climb up on-top a building or location you feel like you probably shouldn't be able to and you find an unlockable. Playing through Borderlands 3 right now and finding chests this way is never not satisfying.

Famous last words. I loathe 4th wall breaks EXCEPT for fodder whining on patrol things like, “I’m itching for some action!” “Nothing to report. Ever.” “Wish they’d show up already.” You can find this many action games, but especially shooters and it never gets old. Edgey 6th gen games really had a lot of this, stuff like Bloodrayne 2 had lines that verged on pornographic. It’s the dumbest shit and it rules.

Kero Blaster and associated short titles also do this and I LOVE it

torchlight pets are the ultimate little guy. every game should have this. they should put it in fifa soccer

God, torchlight II's pet system was so good. Not only were they a cute little guy who helped you in combat, but they were spare inventory that you could send to the shop to sell while staying in the dungeon. Which is like, one of the big issues with the dungeon crawler genre that they basically solved and then everyone ignored that solution.

Like, because they were useful in combat, but not so useful as to be crippling to be away, you could actually engage with this mechanic and it was a risk reward choice. "Is this a good time to send my pet back? I can't carry much more stuff if I don't, but if the area is too intense then I could die and be worse off." It like, created a real attachment to the pet, cause they had several ways they were useful to you.