That mutant that was able to amp people's powers, mutant or not...
Fabian Cortez was his name, he's dead but i remember that he was able to amp Maximus (a fodder telepath) to the point that he one-shotted Blackbolt with a psi blast.
he can be very useful.
There was a Morlock named Boost who could amp powers without the addiction element. He actually became energy and entered the mutant he was boosting.
Gambit never seems to charm anybody anymore, he really hasn't done it since the 1990s in fact.
There was also a mutant introduced in the Iceman solo that could amplify powers. I think he was called Zachary and he also appeared in the Typhoid Mary X-Men/Spiderman/IronFist crossover
Fabian could have been on Hellions. I always read him as queer with daddy issues for Magento. They could really make his power amping a bit more seductive if they wanted to go that direction. Also we have Chance who should appear again.
Devon Alomar never got his time to shine
Chance, from the Fallen Angels mini (who may be trans?) and Cressida, a Sin Congese mutant who amplifies mutants powers a thousand fold at the cost of absorbing the life-forces of dozens of normal humans (a sort of Trevor Fitzroy/Selene cost) who appeared around the time of Never Surrender, are two more examples of that 'boost others' power set.
Technically, Scrambler, of the original Marauders, also seemed to be able to enhance other mutants powers, but more often in the process of causing them to go wildly out of control. Since he could also cause them to go 'out' completely, or even overload to the point of killing their user, I imagine that he could control it sufficiently to be a non-destructive overload, but we never saw him use his abilities to 'boost' his teammates in this manner. (Seeing him 'boost' Sabertooth and evolve him into a massively hypermuscled killing machine with foot-long bone claws and a lion-head could have been interesting...)
Michael Nowlan was another power enhancing mutant. https://marvel.fandom.com/wiki/Micha...an_(Earth-616)
I think a power that has not been shown or at least not to my reading is complete power stealing.As in a mutant like Leech mixed with Rogue,they touch you and depower you,either for some hours,some days or permanently.Meanwhile every power they steal,they keep.Definitely it would be a villain like the Petrelli family patriarch in Heroes season 3.That would be a super dangerous foe if they depower an immortal first