There are other discussions of Apostate's flip ability on the forum (this is the most relevant from a basic search), but I haven't seen this specific question answered in full. Apostate's "destruction effects" are worded slightly differently on each side of his card. I'm pretty sure I know how to handle this, but I've seen some differing opinions and want to make sure I have it right.
If Apostate would be reduced to 0 or fewer HP and there is a villain relic in play, destroy the villain relic with the lowest HP and flip Apostate's villain character card.
Compare to the wording on his reverse:
If Apostate would be reduced to 0 or fewer HP and there is a villain relic in play, instead, destroy the villain relic with the highest HP and flip Apostate's villain character card.
So the question is: Does Apostate actually take the damage before he flips? I would say yes on his Infernal Emissary side and no for the Dark Corruptor. On his Dark Corruptor side, the addition of the word "instead" makes it clear that the damage would be prevented by the relic destruction and he would retain whatever HP he had before he was targeted and flipped. The absence of that wording on his front side, however, seems to indicate that he would take the full damage first.
This is important, for example, for Rooftop Combat or when Absolute Zero is keeping track of the cold damage he has dealt.
Another edge case that would cause trouble is if Apostate has >20 HP on his Infernal Emissary side before a flip is forced. The simplest example has him at 21 HP when Tachyon lands a 21-point Lightspeed Barrage. If he takes all 21 points of damage and then flips then there's no problem; just restore him back up to 20 HP and keep going. If the damage is prevented, however, do the instructions on the reverse side bring him down to 20 HP after he flips?
Thanks for your input.
...yeah, me too.
You are correct, front side he does take the damage and will flip, while on his flip side he will not take the damage and flip.