I won't list fights that fit under the "bigger heroes" umbrella, else we'd be here all day. But looking over the popular villain fights, and restricting it only to either games and/or cartoons (since those are the two big speculated options for this point in the season), AND keeping in mind the assumption next fight after TanJojo is a sprite fight, we've got these as potential options(this isn't a definite list):
Bowser vs Eggman: Probably not. Little too big for a random slot like this, .
Bill vs Discord: No comment.
Nolan vs Bardock: No comment.
Cinder vs Azula: No comment
Skeletor vs Mumm-ra/Lord Zedd: Mumm-ra's the legacy pick, but also isn't as known to casuals as Zedd and has the whole "villain version of a hero fight" going on that has Thawne go up against GB instead of Scourge.
Gru vs Megamind: I'll place my now. If it's a cartoon fight, it'll be this one.
Ridley in general: Dread did quite well last year, so while Ridley maybe isn't super relevant, Metroid in general definitely is. Vilgax is whatever, Vile is based, Rayquaza can step on a Lego.
Vilgax in general: No comment.