If you've seen Slime in MK, Slimer from Ghostbusters comes to mind with the ectoplasm and oozy mucus powers they share. He's just in a ninja-like humanized form (don't want this character in MK though). It's a mystery what he's got to do with Outworld. Virtually no MUGEN (?) fighters make it anyway.
From slimy projectiles he could stick opponents to the ground, side walls or ceiling, leaving them discombobulated. This would be something not seen from him in the MUGEN games like the virulent bubbled thick (slippery) liquid substance that he's known for, which engulf the victim.
I put the (virescent) colour thing with the dermis and that aside. I just refer to it as phophorescence, due to the chemistries in his goo and plasma. This will cause him to sometimes transmute uncontrolled or with proficiency, at times.
I'd be accepting to another character that comes in a male and female, (as a pair). At the same time, couples like this in MK shouldn't be over done.
Old school, Slime and Slimette.
Don't like resorting to Microsoft Bing for images, as he should be featureless, with viscid matter as the outfit.