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

Oak is pretty much a dps check.

He does spam leap slam and Enduring Cry (Regain)
If you move around a lot or if there multiple target he will keep jumping around with leap slam.

There no bug, it his normal behavior.
As said on the previous post. If the regain bother you, you have 2 choice.
-Brute Force (Come back later stronger)
-Adapt (Use Frost Bomb to counter the life regain of enduring cry by 75%)

He was a real pita back in open Beta.. :)

Dropping a bleed on him can help as well.

2024 and he's still fucking unkillable without being able to purchase skill gems, which you can't do at the beginning of a league. Fucking stupid.