The block revive debuff exists!!!
I can't be sure what exactly happened - Mortu used Peril on Ukko, who was Polymorphed. One of two things then happened - either both shots hit the sheep, killing it, and then preventing him from turning back into a human due to Block Revive (which ... is weird, since I wouldn't expect that interaction), or the first shot killed the sheep, then the second shot killed the human - which is also weird, since I don't know why that would result in the debuff being placed. Note that in the info screen, the debuff wasn't visible.
Also, in case you're curious, no, I didn't win. Team doesn't work great vs UDK, weak affinity is just too annoying :/