Actions

Multiattack. The bonestrider makes two attacks; one Bite or Leech attack and a tail sting.   Bite. Melee Weapon Attack: +9 1d20+9 to hit, reach 10 ft., one target. Hit: 21 3d10+5 slashing damage. If the target is a medium or smaller creature, it is grappled (escape DC 17). While grappled this way, the creature is considered restrained and the bonestrider cannot make another bite attack.   Life Leech. A creature grappled by the bonestrider must make a DC 16, on a failure the creature takes 19 or 2d8+10 necrotic damage. The bonestrider regains half the damage dealt, rounded down, as hit points.   Necrotic Stinger. +9 1d20+9 to hit, reach 10 ft., one target. Hit: 18 3d8+5 necrotic damage. The target must succeed on a DC 16

Reactions

Spectral Blur. The bonestrider gains resistance to the triggering damage type until the start of its next turn.

Legendary Actions

The Bonestrider can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The Bonestrider regains spent legendary actions at the start of his turn.   Move. The bonestrider moves up to its speed.   Attack. The bonestrider makes one of the following attacks; necrotic stinger, bite, or Life Leech attack.   Afterlife Blur. Attacks against the bonestrider have disadvantage and it can pass through other creatures as though they are difficult terrain. If it ends its turn inside a creature's space, the bone strider takes 10 force damage and is ejected to an adjacent empty space.

Lair Actions

On initiative count 20 (losing initiative ties), the bonestrider can take a lair action to cause one of the following magical effects; the bonestrider can’t use the same effect two rounds in a row:   Sapping Pulse. The bonestrider sends out a rippling pulse of negative energy. Creatures in the lair must make a DC 15 Constitution saving throw or have their speed halved. If they fail by more than 5, their speed is reduced to 0.   Grasping Dead. The bonestrider causes skeletal arms to rise from an area on the ground in a 20-foot square that he can see. They last until the next initiative count 20. Each creature in that area when the arms appear must succeed on a DC 15 Strength saving throw or be restrained until the arms disappear or until the bonestrider releases them (no action required).   Negative Energy Wave. Creatures within 60 ft. of the bonestrider must make a DC 15 Constitution saving throw or suffer a level of exhaustion.

Usually a bone pit or ossuary of some sort.

Suggested Environments

Underdark, Urban