Volcanic Charge. If the pig 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 10 (3d6) slashing damage. If the target is a creature, it must succeed on a DC 14 Strength saving throw or be knocked prone. In addition, if the target is a creature or a flammable object, it takes 7 (2d6) fire damage and catches fire; until someone takes an action to douse the fire, the creature takes 5 (1d10) fire damage at the start of each of its turns.

Hot inside. Volcano pigs radiate heat, but not intensely enough to cause damage unless their rocky skin is broken. If the pig takes 8 or more piercing or slashing damage from an attack a gout of superheated air and flame bursts from the wound, causing 1d6 fire damage to all targets within 5 feet. However, if a volcano pig takes 5 or more points of cold damage over one round this chills its crusty exterior, cooling its heat gouts enough they cause no damage that round. Once the pig is reduced to 30 hp or less, its cracked hide produces a gout of heat whenever it takes any amount of damage from an attack that does not include cold damage.

Relentless (Recharges after a Short or Long Rest). If the volcano pig takes 20 damage or less that would reduce it to 0 hit points, it is reduced to 1 hit point instead

Water Susceptibility. For every 5 feet the volcano pig moves in water, or for every gallon of water splashed on it, it takes 1 cold damage.

 Multiattack. The volcano pig makes one tusk attack and one snort attack.

Tusk. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 14 (3d6 + 4) slashing damage. 

Snort. Melee Weapon Attack: The volcano pig exhales a gout of superheated gas on one opponent within 10 ft. The victim must make a DC 14 Dexterity saving throw, taking 14 (4d6) fire damage on a failed save, or half as much damage on a successful one.  If the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns.

Lava Bomb (Recharge 5-6). Ranged Weapon Attack: +6 to hit, range 30/120* ft., one target. Hit: 18 (4d6 + 4) bludgeoning damage. The lava bomb then explodes in a shower of lava and incandescent gas; all targets within 10 ft. of the impact must make a DC 14 Dexterity saving throw, taking 14 (4d6) fire damage on a failed save, or half as much damage on a successful one. If the target is a creature or a flammable object, it also ignites if it fails the save. Until a creature takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns.​