My complete list, so far...
k4tzm4n- Jamie Madrox's duplication. Because he seems to be nearly everywhere at once, and he picks up tons of skills and knowledge from other people everywhere he goes.
Morpheus- Adadeus Cho's brain. Because raw logic and rationality is his greatest weapon. He is always right. Always.
Vance Astro- Sebastian Shaw's powers. Because the only possible way to fight him is with skill and precision. The more brute force you use against him, the more he will use right back at you.
Erik- Emotion enhancement. Because he seems to be able to bring out either the best, or the worst, in anyone, depending on how they were already feeling.
Crom- Snowbird's powers. Because he's versatile, highly interested in magic and being a god, and above all else... Canadian.
Strafe- Invulnerability. He does not get riled up or butthurt easily, and the things he says in debates generally can not be argued with.
Spidey 15- Doomsday. Because he can't be beaten the same way twice. You can out-debate him because of his lack of knowledge on one character, but the next time you debate he'll have done his research and he'll know that character just as well as you.
Jake Fury- Bushwacker's powers. Because, honestly, what Alabama man doesn't want to be a radical xenophobe who can turn his limbs into shotguns?
Dane- Midnighter's powers. Strong enough and skilled enough to hang with just about anyone, and is pretty much the world's leading expert on setting up scenarios.
ckal- Sage's internet-brain. Because of his uncanny talent for getting news and updates in the media a week before anybody else knows about it.
InnerVenom- Cannonball's powers. Because he is constantly energetic and lively, and doesn't seem to be easily hurt.
Purrps- Dazzler's powers. Because of her ability to stand out and take the spotlight just about every time she posts.
Oh, and for being hot too
Dedmanwalkin- Vast magical powers (magic is pretty much the loopholes to all the laws of nature) and Noh-Varr's "white running" (focused and unrelenting pursuit of a goal).
No explanation necessary.
NexusOfLight- Bobby Drake, but with electricity instead of ice. Because he's cool and likeable, and his natural talent makes up for any lack of experience.
Wasp's Boyfriend- Sunspot, but with the addition of teleportation. Because he's strong and energetic and doesn't take life
too seriously. And while he's not always the most prominent member in some team-ups, he seems to show up pretty much everywhere.