Grief
To "grief" a mage is to commit acts of violence against the mage for reasons of own personal vendetta; to avenge something the mage or the mage's guild has done previously. Griefing is often done using elements of surprise and/or non-description mages to rob the target of an identifiable source of the attacks.
Griefing usually takes place during armageddon where causing the fall of a potential Hall of Fame candidate is a particularly satisfying revenge, though trans-reset griefing isn't unheard of.