Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny insect. The swarm can't regain hit points or gain temporary hit points.

Amorphous. The abyss swarm can move through a space as narrow as 1 inch wide without squeezing.

Earth Glide. The abyss swarm can burrow through non-magical, unworked earth and stone. While doing so, the abyss swarm doesn't disturb the material it moves through.

Spider Climb. The abyss swarm can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Aggressive. As a bonus action, the abyss swarm can move up to its speed toward a hostile creature that it can see.

Bites. Melee Weapon Attack: +3 to hit, reach 0 ft., one target in the swarm's space. Hit: 10 (4d4) piercing damage, or 5 (2d4) piercing damage if the swarm has half of its hit points or fewer.

Limited Telepathy. The abyss swarm can attempt to mentally attack a creature whose space it enters. After its first turn in the creature's space, the swarm has managed to partially cover the creature and attempts to cause the target to go berserk. The target must succeed on a DC 15 Wisdom saving throw or go berserk.

While berserk, the target must use their action each round to attack the creature nearest to them. If the creature can make extra attacks as part of the Attack action, they use those extra attacks, moving to attack the next nearest creature after they fell their previous target. If they have multiple possible targets, they attack one at random. The creature is berserk until they start their turn with no creatures within 60 feet of them that they can see or hear.