Vaal Oversoul

Vaal Oversoul is the final boss of Act 2, located in Ancient Pyramid

One must use the Complete Amulet from the quest Deal with the Bandits in the Dark Altar in order to summon him.

In the Beta as of 0.9.11, defeating him opens you way into the next difficulty.

Abilities

Lightning Beam

Fires a lightning beam with 100% chance to cause Shock on hit.

Ice Shards

Spreads ice on the floor, causing the player to walk slowly.

Power Slam

A powerful strike to the ground, dealing massive damage.

Summon

Summons monsters.

Hide

Hides in the ground and comes back in a different location. Used mostly after summoning monsters.

Quake

Causes rocks to fall from the ceiling. The rocks will spawn ontop of all players present in the room, as well as other spots randomly in the room afterward.

Strategy

The best counter to his powerful attacks is good mobility. Always pay attention to his movements and see which arm he is using.

The longer and thinner arm is the one that shoots lightning. Dodging this is a must, as it causes Shock on hit and can stack up to 4 times, causing you to take 80% increased damage. Having max Lightning Resistance at this point is vital.

The bigger round arm is the one that he uses for his crush attack. This one is slow and easy to dodge. Having high Armour can help you survive this. If you have the Shock status on you, stay away as you will probably take massive damage from it.

The smaller arm shoots ice shards. It deals little damage but it's mostly impossible to avoid. Try not to walk on the ice to keep your movement speed.

The monsters he summons are dangerous and deal high physical damage. Take care of them as soon as possible, while the boss is hidden away.