Official Errata

Loki should say Forced Interrupt instead of Interrupt. Triggering this ability is not optional, it is mandatory.

Loki is a way harder nemesis to deal with than any of the others. The chance for him to heal with the random mechanic means you really only want to defeat him when you know what is coming or you have no other option and have to hope. Otherwise you are wasting actions and damage unless you get lucky.

I made a Thor deck recently (link here) and played it several times, and Shadow of the Past came out in the first few rounds of over half of these games, so I've had to deal with Loki many times. From this, I've learned a few things about dealing with him that I'd like to share with you:

• Don't forget that when Loki comes out, you get to draw 2 cards from your "Have at thee!" ability.
• Prioritize spending cards and resources on dealing with Family Feud over dealing with Loki, because Thor is better at defeating minions than he is at thwarting. Defender of the Nine Realms works against Family Feud just as well as it does against any other scheme.
• Hitting Loki with Overkill attacks makes sure your damage doesn't go to waste even if he does heal himself back to full. One time I had a lot of fun putting a Marked* on him and just clobbering him over and over.
• Vivian* shuts off Loki's healing entirely! I've been slotting Vivian in all my Thor decks for this specific reason.

*I know Marked and Vivian came out many cycles after Thor, but still.