LOL, I ended up checking the raws because of how messed up the names were, and yep, they're just as weird in the raws. I DID figure out some of them.
"Gilgamesh" was taken (or locked out for a player name), so he did the next best thing:
ギル = Gil
ギノレ= Ginore, but if you imagine the second and third characters are smooshed together, you can see where they got it. It's like using "cl" in place of a "d"
"Monkey Dive Sasuke" is a play on "Sarutobi Sasuke", a legendary ninja. "Saru" = "monkey" and "tobi" = "jump", so someone probably got "Monkey Jump Sasuke" first, and he settled for "Monkey Dive"
"Mentalist" uses kanji for "Menta" (-ta being a symbol used sometimes in male names) and spells "list" phonetically. Just a fun little crossover.