PocChac is a rare Runeword created by combining a Poc Rune of Ritual and a Chac Rune of Invocation.
How to Create PocChac
You can create PocChac by adding the rare Poc Rune of Ritual and the rare Chac Rune of Invocation to a two-socketed 
Helm, 
Chest Armor, 
Pants, or 
Two-Handed Weapon.
Overflow
PocChac can not overflow because the amount of Offering you receive from the Poc Rune exactly fills the required Offering of the Chac Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.
Legions
Helltide