The Chosen Ones

Hello,

First of, as it's my first post on this forum so I'd like to give you my thanks for making this great campaign, I really liked it so far and I'm looking forward to the next updates/chapters. I realize it's a huge project and would like to say great job!

So, I'm having difficulties understanding and beating the mini-boss Ruy [something], the lich character from the archbishop's graveyard in Chapter 7

I have the impression that every time one of his black fellhounds enters through one of the portal he open he fully regenerates his health. I understand you need to hit a portal about three times (or is it a certain amount of hp?) to close it.
It seems too hard to manage to close every portal before any fellhound comes out, so I tried focussing on killing one of the 100k hit points portals. After I did that there was no more portal that appeared but fellhounds still spawned.

Am I missing something? I could really use a hint as to how I'm supposed beat him.

Thanks