I have 2 ideas that, if I could figure modding, I'd want to give a try at making.

One is heavily Percentage based, with Defends giving you Block equal to a % of your max Hp, & Strikes dealing a certain, low-ish percentage of the enemy max Hp ((all end numbers to be given as much fairness as possible))
they would also benefit from removing Buffs from foes, Purifying them.

The other idea is a Powerful Character, with a flaw; The countdown is coming, and can only be held back by purposefully weakening yourself. lots of X-costs with high returns, and some 1-costs that directly and indirectly hinder you, but restore some of the countdown.

the second one would probably be harder, & much easier to 'break', by selling their relic, if a mod that permits that is being used.

any pointers or places to start?