Mercenary healing enemies

SO I got this op mercenary with holy relic and consecrated path, and lately as i got into t16s (and my damage isnt at the point where i can kill bosses quick enough), I have been noticing the map bosses regenerating life/healing ALOT.
Literally outhealing my damage. In all the cases where this happened none of my map modifiers had anything that would allow or make the bosses heal or regen. Even less this much.
I believe the mercenary is healing them. If someone has some insight on this please let me know.
Thank you.