AhuXal is a legendary Runeword created by combining a Ahu Rune of Ritual and a Xal Rune of Invocation.
How to Create AhuXal
You can create AhuXal by adding the legendary Ahu Rune of Ritual and the rare Xal Rune of Invocation to a two-socketed 
Helm, 
Chest Armor, 
Pants, or 
Two-Handed Weapon.
Overflow
AhuXal can not overflow because the amount of Offering you receive from the Ahu Rune exactly fills the required Offering of the Xal 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