Upper. When Grendel would take lightning damage, his Overpower and Relentless Endurance features immediately recharge.   Lightning Absorption. Whenever Grendel is subjected to lightning damage, he takes no damage and instead regains a number of hit points equal to the lightning damage dealt.   Relentless Endurance (Recharges after Finishing a Short or Long Rest). When Grendel is reduced to 0 hit points but not killed outright, he can drop to 1 hit point instead.   Pack Tactics. Grendel has advantage on attack rolls if at least one ally is within 5 feet of the creature he's attacking and the ally doesn't have the incapacitated condition.   Brute. A melee weapon deals one extra die of its damage when Grendel hits with it (included in the attack).   Raw Agility. When Grendel moves on his turn in combat, he can double his speed until the end of the turn. Once he uses this trait, he can’t use it again unless he moves 0 feet on one of his turns.   Charge. If the Grendel moves at least 10 feet straight toward a target and then hits it with a melee attack on the same turn, the target takes an extra 11 (2d10) damage. If the target is a creature, it must succeed on a DC 17 Strength saving throw or be pushed up to 10 feet away and knocked prone.