u/MaleficTekX

Among these we have:
-Sudowoodo with stretchy legs.
-All dragon types can make invisible vapor trails that when the intersect make invisible platforms.
-Kyogre and Groudon are Eldrich horrors that can possess you if you touch their favorite rock.
-The legendary Beasts drain all the oxygen in the area when they fight together.
-The Regi’s can hold back world destroying blasts for 20 days straight
-Deoxys can drive rocks at 980,000x light speed
-Mewtwo Spoon
-the Tao Trio can pull you into the Dream World or attack you on the outside from within it.
-Psychic types can invade technology.
-Substitute is a perfect clone that can become a surfboard.
-Everything Ice related from GSC.
-Hyper beams that are Omega Beams.
-Arbok patterns.
-Everything regarding Regigigas.
Probably will think of more later. I love manga BS.

In the manga, a mega stone is stolen from a mega who can use the item, Necrozma straight up steals the z crystal it needs to transform from across time and space, and despite the blue orb not being an explicit transformation item in gen 3, it does transform the holder in the manga and fuse with them. (Basically it turns you into Kyogre and Groudon. That’s fun)

Additionally Looplets/Emera which allow mega evolution can be stolen or knocked off in Mystery Dungeon

Zygarde, you’re a goat, but this cat swam an ocean just to get revenge on this loser, and then left him to get eaten by aliens. Dollar, is the GOAT