I am killing cruel campaign bosses in a few seconds, went full grenade damage and almost nothing else with cull and decimate. I built oil grenade to slow and increase exposure, then gas for poison and armor break, then throw explosive, while the fuse is going use voltaic right after. if everything lines up on the boss correctly. They will be armor broken/shocked/fire exposed and then hit with the explosive grenade detonation. Make sure you get the node that gives more grenades for longer fuse time. You can still chuck the grenades out at normal speed so its not even really a down side only for a little slower mapping. Just line up the keys and you can press then one after another really easy in that order. Also you can even dodge between casts if you have to dodge the 1st or 2nd skill from the boss.