Once you have prepared as much as you can/want to. Begin the fight by preferably seperating Dallis far from her goons into a location you already prepared for your allies/party to ambush her at, with hopefully a massive field of oil in between her goons and that location. But make sure...
depending if you let him escape in Act 2. Kill everything and talk to the spirits you will find in this room. There are 3 important books on that big table you can't miss. Make sure you read:
The first stage of the fight ends when Dallis the Hammer's health points are reduced drastically. The final fight in Divinity: Original Sin 2 is rather easy, provided that you have prepared yourself. You should equip your party with a lot of abilities that use Source Points - you have an...
Just kill them all and run to the end and watch the cutscene where Dallis the Hammer suddenly appears and denies you the power. The arena will collapse and you will have to face your raging gods that will attack you with a copy of yourself. The last embodiment of the god that is still...