Tail Spike Regrowth. The abyssal manticore has twenty-four tail spikes. Used spikes regrow when the manticore finishes a long rest.

Maddening Whispers. The abyssal manticore telepathically whispers incoherently while it can see any creature and isn't incapacitated. Each creature that starts its turn within 20 feet of the abyssal manticore and can hear the whispers must succeed on a DC 10 Wisdom saving throw. On a failure, the creature can't take reactions until the start of its next turn and the DM rolls a d4 to determine what the whispers say.

On a 1, the whispers tell a truth about the creature that they have no knowledge of.

On a 2, the whispers tell a truth about the creature that they have knowledge of. 

On a 3, the whispers tell a lie to the creature.

On a 4, the whispers are random and chaotic giving the creature no insight.

These whispers could be about the past, present, or even the future. What the context of the whispers are, and how much information is given is to the DM's discretion.

Multiattack. The abyssal manticore makes three attacks: one with its bite and two with its tentacles or three with its tail spikes.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage.

Tentacle. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) bludgeoning damage.

Tail Spike. Ranged Weapon Attack: +5 to hit, range 100/200 ft., one target. Hit: 7 (1d8 + 3) piercing damage.