So many heroes are balanced around damaing themselves that I consistently feel that this Writhe is one of the best cards in the game and absolutely crushes opponents in any mode. Some quick examples I've found of how to use him:
1. Golem Unity - Free Bots all day every day! It changes her power to "play a bot!"
2. Setback - I like to get an absolute ton of unlucky tokens in the pool. Writhe can turn off that 3 damage for Looking Up, then later on, Destroy LU for an insane Cause and Effect turn. Do this to Iron Legacy for extra fun.
3. Dr. Medico likes to beat the crap out of himself to heal others, but until he has Experimental Medicine, the damage is really just optional. Let Writhe keep him nice and healthy until then.
4. Prime Wardens Fanatic - Already one of the strongest powers in the game, this makes her read play the top card of her deck and grant a power without a drawback. It also makes Embolden a way better play on this version, as taking only 2 from that for the 2 power uses instead of five is amazing.
5. Extreme Prime Wardens Haka - Redirect and heal without taking damage. Thanks! It also finally lets me play Enduring Intercession which used to be discard fodder.
6. Idealist - Now, Id is just a damage boost.
7. Any Legacy - Heroic Interception? Every turn if you can! He's immune to first damage, everyone else is immune to all damage. Take down not hurting Legs is pretty solid too sometimes.
8. Nightmist - the power reads draw 2 while she gets set up, and when she is, it lets you just use Heedless lash... heedlessly, among others. Draw for no damage and destroy X ongoing with no damage are pretty amazing too.
9. Ra: Setting Sun: Deal 2 irreducable to everything and don't bother hurting yourself.
10. Prime Wardens Tempest - Now it's just 1 free card play.
11. Visionary - Wrest the mind is quite punishing, but not when the redirect is free!
Writhe takes some of the strongest cards and characters in the game and utterly busts them. I think Cosmic Inventor Writhe is one of the best characters in the game. What else can he do?