Charge. If the boar moves at least 20 feet straight toward a target and then hits it with a tusk attack on the same turn, the target takes an extra 7 (2d6) slashing damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.

Relentless (Recharges after a Short or Long Rest). If the boar takes 10 damage or less that would reduce it to 0 hit points, it is reduced to 1 hit point instead.

Deathly rage 

The boar scores a critical hit,on 18-20.

Tusk. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) slashing damage.If this attack scored a critical hit, and rage of the dragon is not active, then rage of the dragon triggers.

Rage of the dragon

Until the start of it's next turn ,the boar enters a primal state of rage.While in this rage, it is resistant to all damage, except fire, force and psychic damage, and is immune to fire damage.In addition, if it scores a critical hit hit during the rage, the attack deals an extra 1d6 fire damage.