Bone Boar

Bones. The Bone Boar being just a boar skeleton allows for it to swim in water at the same speed as it walks.

Relentless (One Time Use Per Rest). If the boar takes 7 damage or less that would reduce it to 0 hit points, it is reduced to 1 hit point instead.

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 1d6 slashing damage. If it uses a boar charge attack instead and if the target is a creature, it must succeed on a DC 11 Strength saving throw or be knocked prone.

Boar Charge. The Bone Boar is forced to use up its remaining movement speed to go forward in a straight line. Any creature in its path must make a dexterity saving throw (DC 13 increases by 1 each level of the caster) or take 1d6+1 bludgeoning damage. If the creature succeeds on the dexterity saving throw, they avoid all damage and effects.

Tusk. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit: 1d6+1 slashing damage.