TamThul is a legendary Runeword created by combining a Tam Rune of Ritual and a Thul Rune of Invocation.
How to Create TamThul
You can create TamThul by adding the legendary Tam Rune of Ritual and the rare Thul Rune of Invocation to a two-socketed Helm, Chest Armor, Pants, or Two-Handed Weapon.
Tam - Cast a non-Channeled Core Skill. (25)
Thul - Invoke the Sorcerer's , inflicting Freeze and Vulnerable onto enemies. (400)
Mystical Frost Nova
Overflow
TamThul can not overflow because the amount of Offering you receive from the Tam Rune exactly fills the required Offering of the Thul Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.