Amber-Shaper Un'sok and Guardians (probably Ferals as well)
Not sure if someone posted this already but it seems that there's a bug with Reshape Life casted on bears (and prolly cats) which results in them being able to use leader of the pack heals while being shaped. This results in huge heals that construct is receiving while maintaining debuff on boss which significantly increases damage needed to bring it down to 20%. If someone wonders, shifting out of bear 1s before he finishes his scalpel channel works as a temporary workaround.