Baby Frank

This is essentially just what I found to be the most effective build for Ur-Sek. He is my favorite species of voidling, so I made it a point to use it consistently. The idea is pretty simple: be super tanky, and do a lot of damage. The sustainability from Abyssal Grasp combined with the damage from Cursed Pact works to provide strong survival. You can ultimately use whichever third perk you prefer, however, I went with Super Speed as I prefer fast gameplay. But it would be interesting to see how far this build could go with some kind of revival perk.

I have found this build combination to be the most successful. I've pushed this build to around Abyss Level 60. I imagine you could bring this build to the moon with consistency, and a solid third perk. The trick is maximizing your combat time to limit any health loss from damage intake. As long as you are swinging, you will also be healing. I also suggest switching to Ur once you hit around level 50 for more survivability.

Enjoy!