This is mayhem mode. I think most of Diggie's mayhem buffs are hidden, so you won't see them in the ability descriptions. But there are two that I've seen:

First, 1. Diggie's egg spin has a random chance to do a massively increased amount of true damage. The chance and amount of damage increases with level, I think.

And 2. Certain on-hit items now work on Diggie's skills. Most important are Lightning Truncheon and Necklace of Durance.

Lightning Truncheon gives you additional damage on your skills every six seconds that scales with mana. My Diggie build gives a fuckton of mana, so this is going to be a lot of damage. And Necklace of Durance reduces healing when you hit with skills. So in total, you're reducing the enemy healing in their own base, dealing random amounts of massive true damage, and also dealing some sizeable Lightning Truncheon damage every six seconds.

End result: sometimes you can 100-0 enemies in their own base.