Nightmare Pursuit: The hound can hunt creatures while they sleep, splitting into a pack and attacking them in their dreams. The hound must be linked to a creature to enter its dreams by having seen the creature on a physical plane or being cast into their dreams through a Dream spell. A link can be broken through a Dispel Magic or Remove Curse spell.
Prismatic Form: The hound sheds a dim light for 10ft that causes its image to split and repeat. This effect lasts until the hound is hit by an attack or is reduced to 0hp. While it lasts attacks against the hound have disadvantage its attacks have advantage and, if the effect is present at the start of its turn, it can make an extra claw attack. The effect resets at the end of the hounds's turn or if it would take radiant damage. Additionally the hound has advantage on Stealth checks made while in bright light.
Multiattack: The Prism Hound makes two attacks, one with its bite and one with its claw, plus an additional claw attack if its Prismatic Form ability is present at the start of its turn.
Bite: Melee Weapon Attack: +7 to hit, reach 5ft, one target. Hit: 9 (1d8+4) piercing damage plus an additional 4 (1d6) radiant damage.
Claw: Melee Weapon Attack: +7 to hit, reach 5ft, one target. Hit: 8 (1d6+4) slashing damage
-----------------------------------------------------------------------------
Nightmare Form: The hound loses its Prismatic Form in favor of appearing as a massive pack of its mirror apparitions. Each member is of the pack is modified in the following ways:
12 AC 9HP (1/10 of total) +5 to hit, and +2 to damage
The assault starts with two members of the pack attacking and one more converging on the target each round until the target dies or the hound is pushed out of the dream. It is pushed out of the dream when 3 members of the pack are slain or the link is broken from outside the dream.
The Prism Hound makes one Reaping Slash attack for each member of the pack converged on the target.
Reaping Slash: Melee Weapon Attack: +5 to hit, reach 5ft, one target. Hit: 5(1d4+2) necrotic damage and the target's maximum hit points are reduced by the damage taken.