[M3T4L V1KING]

MU Variants (That I'm aware of):

Series 1:

Dark Red Daredevil
Dark Blue Bullseye
Dark Blue and White Human Torch
Black Costume Ronin
Black Dragon/Closed Hand Iron Fist
Dark Blue and White Thing
Dark Ms Marvel (Karla Sofen)
Glossy Red Hulk
Glossy Electro
Upside Down Packaged Spider-Man

Series 2:

Wave 6 New Head Mold Wolverine (Wasn't aware of this one actually)
X-men Costume Warpath
Phasing Vision
White Shirt Luke Cage (Idk the story on this one)
Yelena Belova Black Widow (Idk what's going on with this one either)
Death Mask Archangel
Classic Havok
Norman Osborn Head Iron Patriot
Long Hair Winter Soldier
Skrull Language Stand Skrull Soldier (Never seen or head of it before)

Series 3:

Cable w/o Hope (Running change)
Astral Doctor Strange
Upside Down Packaged "Spider-Man" stand Scarlet Spider
Son of Hulk Stand Skaar
Paint Variant Darkhawk
Imperius Rex stand Sub-Mariner
Iron Man Nameplate Tony Stark
Human Skinned Absorbing Man (Or Metal skinned, it's debatable)

And I think that's all of them... for the single carded ones anyways. Some might say that Classic Ms Marvel and 'Flame-on' Human Torch were variants but since they got their own figure number they're technically not variants.