YaxTal is a magic Runeword created by combining a Yax Rune of Ritual and a Tal Rune of Invocation.
How to Create YaxTal
You can create YaxTal by adding the magic Yax Rune of Ritual and the magic Tal Rune of Invocation to a two-socketed Helm, Chest Armor, Pants, or Two-Handed Weapon.
Yax - Drink a Healing Potion. (100)
Tal - Evoke the Spiritborn's Pestilent Swarm, dealing damage to enemies. (100)
Overflow
YaxTal can not overflow because the amount of Offering you receive from the Yax Rune exactly fills the required Offering of the Tal Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.