When PVP comes out,
It would be cool to have different leagues based on the number of monsters you want to bring.
4, 8, 12 and 16.
There should also be a limit league similar to pauper format in Magic the gathering.
While there may be 900 monsters, the vast majority of them are identical but belong to a different element. This would be a huge overall, but maybe you could experiment with making each element unique. Each element would have its own set of skills, rather than having them all be the same. Maybe that’s too extreme of a change but it would be cool.
And lastly I just wanted to say that I read the admins post on the Pay 2 Win forum where he said that they were inspired by Shin Megami Tensei and I think that’s awesome because that is one of my favorite game series of all time. Kudos.