 If you liked
Konjiki no Gash!!
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 ...then you might like
Shinrin Ouja Moriking
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Both series follow non-human (but mostly humanoid) fighters who take part in a competition for the kingship of their world. In both series, the king candidates pair with humans and fight against other pairs to win the title (though this is not mandatory in Moriking).
Comedy is a big aspect in both series, though Moriking tends to be more a comedy-centered series than the more battle-heavy Zatch Bell.