Here’s some ideas for new powers (I did search to see if there was lots of this already, apologies if it’s old hat)
Achilles heel - the weak/strong cycle between red, green and blue is reversed
Clone with the Wind - the hero mimics the exact stats and powers of a chosen enemy
Pyrrhic victory - the hero and a randomly selected enemy both instantly perish
Burn the Witch! - the next three heroes on either side that fire off a special catch fire causing damage for X turns
Mutiny! - all the enemy troops stats are added to your team.
Absolute Zero - either team randomly becomes Zero’s current team for three turns!