I have Musashi, and his skill description says that for 5 turns, he will heal 50% of the normal damage done. I always read that as meaning that for any damage done by yellow shields/tiles that get sent up the screen, he would heal himself with half of the damage dealt.
I’ve been using him for quite a long time, and he has NEVER gotten any health back for any damage done by by yellow or any other tiles. However; when his skill is still active, any yellow tiles that I send up, seem to give back between 3 and 4 times the normal mana when they make contact. To be clearer, upon contact, they regenerate mana instead of health.