Friend of mine and I defeated Ambuscade. I played Haka, he was Fanatic (the promo version). I think if we couldn't heal ourselves, it might have been over before it began. Savage Mana is the biggest thing that helped us because I was able to consume his cloaking device so he could no longer be invulnerable on his B side. It was very close though. We ended up Haka 7, Wraith 6 and probably one of us would've died the next turn. I'm almost mad I didn't get the challenge where each hero has 5 or less and survives, but I'm good enough with Two Man Army.
Oh yeah. We were in the Realm of Dischord. Not recommended for this challenge. That was my bad idea.