Mount (domestic only). Bristlebacks have been trained to act as mounts for creatures smaller than them, a willing bristleback can be mounted using half your movement speed. The initiative of a bristleback changes to match yours when you mount it. While mounted, it moves as you direct it, and it has only three action options: Dash, Disengage, and Dodge. A bristleback can move and act even on the turn that you mount it. If an effect moves your bristleback against its will while you're on it, you must succeed on a DC 10 Dexterity saving throw or fall off the bristleback, landing prone in a space within 5 feet of it. If you're knocked prone while mounted, you must make the same saving throw. If your bristleback is knocked prone, you can use your reaction to dismount it as it falls and land on your feet. Otherwise, you are dismounted and fall prone in a space within 5 feet it.   Quills (wild only). Any creature that makes a melee attack within 5 feet of the bristleback must make a DC 13 Dexterity saving throw or take 7 (2d6) piercing damage. Any creature that attempts to grapple the bristleback takes 7 (2d6) piercing damage when they make the attempt and at the start of each of their turns they maintain the grapple.   Charge. If the bristleback 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.   Charge (mounted only). If the bristleback moves 20 feet straight toward a target and the rider hits it with a Lance melee weapon attack on the same turn, the target takes an extra 2 (1d4) bludgeoning 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 bristleback takes 10 damage or less that would reduce it to 0 hit points, it is reduced to 1 hit point instead.