Monster Park Extreme boss continuously healing?

What I recall is not that boss healing every 5-10 seconds, but rather regenerating once killed. I didn't usually leave more than a minute to kill the boss, since that is more than sufficient for the rhino boss which is the weakest of the bosses, so i don't know if there was a limit to how many times it could regenerate. At least twice though. If you are abled to kill it repeatedly every 5-10 seconds, you are vastly more powerful than any of my link mules.
Edit: I don't recall Thanatos doing the same thing. I think at least one of my mules could kill it in time.

Poison Golem has 3 forms, much like that one in the PQ. Give yourself enough time to kill 3 forms of slightly increasing difficulty.

Hadriel