Van Richten's Guide to Ravenloft (5e)
Compression. The boneless can move through any opening at least 1 inch wide without squeezing. It can also squeeze to fit into a space that a Tiny creature could fit in.
Unusual Nature. The boneless doesn't require sleep.
Multiattack. The boneless makes two Slam attacks. If both attacks hit a Large or smaller creature, the creature is grappled (escape DC 13), and the boneless can use Crushing Embrace.
Slam. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) bludgeoning damage.
Crushing Embrace. The boneless wraps its body around a Large or smaller creature grappled by it. While the boneless is attached, the target is blinded and is unable to breathe. The target must succeed on a DC 13 Strength saving throw at the start of each of the boneless' turns or take 5 (1d4 + 3) bludgeoning damage. If something moves the target, the boneless moves with it. The boneless can detach itself by spending 5 feet of its movement. A creature, including the target, can use its action to try to detach the boneless and force it to move into the nearest unoccupied space, doing so with a successful DC 13 Strength check. When the boneless dies, it detaches from any creature it is attached to.
Any climate or terrain