User blog comment:PacmanIsGr8DontH8M8/The Pit of Pending Participants/@comment-26330785-20150731214206

Well, I've actually created a list of my own on my profile in regards to who could go into battles, but don't exactly have a suitable combatant. Plus, several options are already taken. Anyway, here's some of my list:

Valentine

Dark Gundam (Was going to put against Megatron, but not only is it 3× bigger in its final form, but it had the potential to host the island of Japan in space and nearly destroyed Earth)

Psyco Gundam (Was going to put against Grimlock, but it's the size difference which puts me off)

Silver Gospel

Frieza

Q

Seryu Ubiquitous

Ilias

Vali Lucifer

Korosensei

Lord Death

Meliodas

Those are just a few, but personally, I think it's a little harder to find an opponent for a character that's not well-known.