So, Xisuma's name origin comes from the word Music backwards with some lettere changed around. Therefore I propose Evil Xisuma's name to be Exnelys, because the evil villain deserves a name of their own.
The opposite of music is Silence
Exnelys turned around is Sylenxe, so its the same but with a few letters changed around.
Also, Xisuma is often shortened to X and Evil Xisuma is shortened to EX. With the name Exnelys that also makes sense