Enemy energy cost of "mend" is too low and heals all enemy health, this can lead to long (10+ turns) battles against regular Blue oni soldier as they keep healing and never run out of energy.
I'm not saying this makes battles hard, but it makes some take longer than they should.
I actually defeated Gozu and Mezu in fewer turns than some regular Blue oni soldiers because I was running low on ofuda cards and Sparky alone wasn't causing enough damage to get through their healing.
I'm also not implying they should lose their ability to heal, but perhaps run out of energy after 3 uses? Or maybe not healing the entire health bar but only a portion?