During any Start of Turn sub-phase, Thorgrim may set the Grudgestone. Once set, Thorgrim and any unit he has joined gains the Unbreakable special rule and automatically passes any Panic tests they are required to make. However, once the Grudgestone has been set, Thorgrim and his unit cannot choose to Flee as a charge reaction and cannot move other than to Give Ground, to make a follow up move or to reform.