I can't kill Oak! (Super health regen????)

Ok, in 3.15 and trying to kill Oak (One of the bandits in Act 2)
I am a templar Using Leap Slam with Earthbreaker and Onslaught along with Searing Bond, Also using ground Slam myself and Purifying Flame w/ Elemental Proliferation and Summon Phantasm Support. Also Flame Dash with Stun Support and lastly Summon Holy Relic.
Most of my passive tree is focused on things like attack damage and speed etc. (That whole square area Northwest of the templar start area)
I can clear maps really easily now with mostly just the Leap Slam Earthbreaker and Searing Bond.
But OAK apparently has some new HUGE Health regen. I can fight and fight and fight and can't hardly even get him off full health longer than a few moments then his life shoots back up to the top. I tried switching the leap slam and the ground slam with no difference. He can't seem to kill me either. So since the gate closes when you start the fight there was no way to ever end the fight other than to stand there and let him kill me or to log out, which I did.

Should this be posted under bugs? This does not seem right at all!

I just killed him with Molten strike on a 2L and Decoy totem.

So I just went back later when I was stronger and completely wiped the floor with oak in a few seconds. I was also lucky enough to have Einhar helping me, so it's hard to make a good comparison.
But I know never in my PoE experience have I ever seen any creature, even the highest of bosses have the kind of life regen that Oak had in that first fight. Especially not without them stopping to cast some kind of spell to gain life. I truly thing it was bugged the first fight. Is it possible for a forum moderator to move this post to Bug Reports forum? Or maybe it was just a one time thing that doesn't matter.
On a side note, after I killed Oak, I ran into a creature called Slenderfang the Ruinous and he was having absolute seizures and convulsions. Maybe something is up with the wetlands? :D

There was a bug with Oak in Ritual I think where he was un-killable.

Unlucky I guess?

When dealing with bosses with high life regen, or with Maven witnessing a map boss, Frost Bomb is your friend with it's reduced regen rate!

No it didn't have anything to do with needing to use a different attack. I'm convinced now it was glitched. One thing I hadn't mentioned was that in that first fight, oak seemed to be using Leap Slam. Almost if not Exclusively. Was jumping all over the place. Didn't see it doing that when I came back later.
Since I had Leap Slam and also had consecrated ground via Purifying Flame, I think maybe Oak was copying some of my abilities?

No he has Leap Slam as an attack.

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Bjorn_Angannon wrote:

When dealing with bosses with high life regen, or with Maven witnessing a map boss, Frost Bomb is your friend with it's reduced regen rate!

You sir, can be my wingman, anytime! You were right. My best friend from Germany goes my SQR had told me about this and I could not find the convo we had when he told me about 2 leagues ago so I couldnt confirm this to help me.

I searched and found 1 post similar to this on reddit but, he just said use this skill then a decoy totem and didn't elaborate enough info to make sense of his post.

I ran into this this morning and you explained it detailed which helped and made sense, I can confirm this does work. You also do not need to use spell cascade although it probably would be even more helpful, you also do not need a decoy totem if your quick enough.

I killed him using only the Frost Bomb and Shrapnel Ballista since I was running Ranger. Thanks again.

There is no bug.

It is the buffed endurance cry so that it became a dps check

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Bjorn_Angannon wrote:

When dealing with bosses with high life regen, or with Maven witnessing a map boss, Frost Bomb is your friend with it's reduced regen rate!

Worked like a charm! Thank you, sir!