NocThul is a rare Runeword created by combining a Noc Rune of Ritual and a Thul Rune of Invocation.
How to Create NocThul
You can create NocThul by adding the rare Noc Rune of Ritual and the rare Thul Rune of Invocation to a two-socketed Helm, Chest Armor, Pants, or Two-Handed Weapon.
Noc - Inflict a Crowd Control that isn't Slow or Chill. (10)
Thul - Invoke the Sorcerer's , inflicting Freeze and Vulnerable onto enemies. (300)
Mystical Frost Nova
Overflow
NocThul can not overflow because the amount of Offering you receive from the Noc 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.