Design: Mojo's one of those Japanese dolls (think voodoo). It's creative, I guess.
Combat: He gets some use early on, but his final tech is mostly overlooked since players are using other characters by that point...
Tilt: Mojo's a pretty fun character. His Japanese name lent itself to this feeling (Lucky Dan), as does his spirit. Surprisingly, he's revealed to be a curse doll, and then completely reinvents himself as Mojoy. He also gets a smidgeon of development if taken to see his "brother" in the yard in Termina in front of the old Glenn / Dario cabin. Even further, there's a line where he says "...I hate-om you" to Poshul, but since he can't be recruited before Cape Howl, this scene can't be accessed (without GS).
These things make him a B. In a world of Acacians, Chronopolitans, Porreans, and El NidoCHA residents, Mojo's a pretty interesting entry.