Berserk. Whenever the lyssatherium starts its turn with less than all its hit points, roll a d6. On a 6, the lyssatherium goes berserk. On each of its turns while berserk, the lyssatherium attacks the nearest creature it can see. If no creature is near enough to move to and attack, the lyssatherium attacks an object, with preference for an object smaller than itself. Once the lyssatherium goes berserk, it continues to do so until it dies or regains all its hit points.

The creature's allies, if within 60 feet of the berserk lyssatherium, can try to calm it by speaking firmly and persuasively. The lyssatherium must be able to hear the speaker, who must take an action to make a DC 15 Charisma (Persuasion) check. If the check succeeds, the lyssatherium ceases being berserk. If it takes damage while it still has less than all its hit points, the lyssatherium might go berserk again.

Reckless. At the start of its turn, the lyssatherium can gain advantage on all melee weapon attack rolls during that turn, but attack rolls against it have advantage until the start of its next turn.

Shapechanger. A creature drops any equipment it is wearing or carrying when it transforms into a lyssatherium. It reverts to its true form at the end of one hour, regardless of whether it is alive or dead.

Wounded Fury. While it has 40 hit points or fewer, the lyssatherium has advantage on attack rolls. In addition, it deals an extra 10 (3d6) damage to any target it hits with a melee attack.

Multiattack. The lyssatherium makes two claw attacks.

Claw. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) slashing damage.