Step 1
First off you pull him out to far right edge of the water against the wall.
Step 2
When Ursine Slams his feet down you knock him down and disarm him. A blue bubble will come up under his name, it is a 30 sec shield so he cannot be knocked down, stunned or cc. You will have to repeat this every time the shield goes away.
Step 3
A WP or DOK needs to Group cleanse everyone constantly so Ursine cant steal AP from everyone and Heal himself. During these group cleanses he may heal a little but your dps needs to be greater then what he can heal himself by, the stats on how much he can heal for we still don't know.
Warning
Melee DPS or anyone within range of him or attacking him can be drained for AP, the npc's attack acts as a proximity drain, so anything that attacks him or is near him needs to be cleansed so he does not steal their AP to heal himself.
Id Like to thank Ozs from Shadows of Divinity and other members from my guild for helping figure this out. I heard a lot of complaints so I decided to look into this boss. I must say it was fun and reminded me of the old times trying to figure out lost Vale and TOVL bosses in live

If anyone can add any further information or if anyone wants us to research any further bosses let me know. Also let me know if this was helpful or not. This is my first feedback post.