Undead Fortitude. If damage reduces the horse to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant. On a success, the horse drops to 1 hit point instead. Vampire Weaknesses. The horse has the following flaws: Harmed by Running Water. The horse takes 20 acid damage when it ends its turn in running water. Stake to the Heart. The horse is destroyed if a piercing weapon made of wood is driven into its heart while it is incapacitated. Sunlight Hypersensitivity. The horse takes 20 radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.
Bite.Melee Weapon Attack: +6 to hit, reach 5 ft. Hit: 6 (1d6 + 3) piercing damage plus 7 (2d6) necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the vampire regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. Target must roll a constitution saving throw (DC 15) or be turned into a vampiric horse. Kick. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: (2d8 + 3) bludgeoning damage.