Coal Fur Bison

Charge: If the Coal Fur Bison moves at leat 30ft in a straight line it can make on additional Basalt Horns attack as a bonus action, if this attack hits the target must succeed in a DC 15 Strenght saving throw taking an additional 2d10 bludgeoning damage + 2d6 fire damage and falling prone on a failure.

Coal Fur: Whenever the Coal Fur Bison would take fire damage it instead bursts in flames, All creatures that end their turn within 5ft of it must succeed in a DC 15 Constitution saving throw taking 3d6 fire damage on a failure, half as much on a success.

This fire remains until the Coal Fur Bison dismisses it (no action required)

Creatures grappling and being grappled by the Coal Fur Bison while its fur is ablaze take 3d6 fire damage at the end of their turn.

Blaze Trail: If the Coal Fur Bison has its Coal Fur trait active it leaves a track of flames where it moves throw. 

This area remains in fire until the start of the Coal Fur Bison´s next turn.

All creatures that move to or end their turn wihtin this area must succeed in a DC 15 Dexterity saving throw, taking 3d6 fire damage on a failure, half as much on a success.

Elemental Beast: The Coal Fur Bison is considered a beast and an elemental for effects that require either creature type.

Basalt Horns: Melee Weapon Attack +7 to hit, 5ft reach, one target, for 2d10+4 bludgeoning damage + 2d6 fire damage.

Flaming Hooves: Melee Weapon Attack +7 to hit, 5ft reach, one target, for 2d8+4 bludgeoning damage + 2d6 fire damage.

A creature hit by this attack must succeed in a DC 15 Strength saving throw falling prone on a failure.

Hoove Kick: Whenever a creature moves while within 5ft of the Coal Fur Bison it can as a reaction make a Flaming Hooves attack against that target.