I didn't even know it was possible, to be honest. But apparently it is.

Just randomly I fought someone named Ap0KaLi and tried to take out their Elhain because Elhain does a ton of damage. To my chagrin, I failed. I thought it was a fluke the first time Elhain dropped to a sliver of health, but then she tanked a hit at that sliver without taking any visible damage.

I'm fairly certain this is a hack as opposed to an in-game effect. Elhain had healed from lifesteal, so it's no set bonus, and the user is level 39 so I'd like to believe it's not some sort of mastery I'm not privy to. Even then, I don't believe any mastery lets you survive fatal blows more than once on separate turns. No Unkillable buff was in play - the rest of the team was Spirithost, Sinesha, and Doompriest, who can't cast that.

If naming the cheater here violates some policy, I apologize. Tell me where I should send this complaint to in that case. I hope you'll ban accordingly - these kinds of cheats make the already-tedious arena blatantly unfair, as there's no way to tell they're cheating until it's too late.