Swarm of Wharflings 2014
CR 3 beast
Large beast, Unaligned
The swarm of wharflings can breathe air and water.
A creature that attempts to move out of or through the swarm of wharflings must succeed on a DC 13 Dexterity saving throw or take 7 (2d6) piercing damage.
The swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Tiny wharfling. The swarm can’t regain hp or gain temporary hp.
Actions
Melee Weapon Attack: +5 to hit, reach 0 ft., one creature in the swarm's space. Hit: 28 (8d6) piercing damage, or 14 (4d6) piercing damage if the swarm has half of its hp or fewer, and the target must succeed on a DC 13 Dexterity saving throw or lose one item it is wearing or carrying to the swarm, provided the item weighs no more than 10 pounds, isn't a weapon, and isn't wrapped around or firmly attached to the target, such as a shirt or armor.
Source: Tome of Beasts 1 (2023 Edition) (Kobold Press) · License: OPEN GAME LICENSE Version 1.0a details