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