This is Shade, Rogue's first ever friend in...

20 equine years...? 

Anyway, Shade is part of a race called the Dragon-Cats. They were created 100 years after the End of Humanity. A few generations ago, his past self got mutated after a nuclear meltdown, the same meltdown that killed Rogue's family. Ever since then, Shade has always been a mutant. Now he has to wait until he dies before he can reunite with his sister Fire Stripes.

One night, during the second war of the Multiverse, he vows in battle:

"One day, this world will be green...

"And the earth will be spilled with your blood."