Necrosteed (5e Creature)
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Large undead, chaotic evil
Trampling Charge. If the necrosteed moves at least 20 feet straight toward a creature and then hits it with a hooves attack on the same turn, that target must succeed on a DC 14 Strength saving throw or be knocked prone. If the target is prone, the necrosteed can make another attack with its hooves against it as a bonus action.
Hooves. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage.
Illusory Appearance. The necrosteed covers itself and anything it is wearing or carrying with a magical illusion that makes it look like a living creature. The illusion ends if the necrosteed takes a bonus action to end it or if it dies.
Occasionally, when a mount is abused to the point of death, the beast's lingering malice towards its abuser causes it to linger in the world as an undead horror called a necrosteed. Almost any mount can become a necrosteed, though the majority of necrosteeds were horses in life.
Vengeful Steeds. A necrosteed's only goal is the death of the person who abused it. It will track down this person tirelessly, as it doesn't need to pause to perform any biological functions, such as sleeping or eating. When its former master is dead, it will continue killing until it is destroyed.
Undead Nature. A necrosteed doesn't require air, food, drink, or sleep.