Banderklown

Ambusher. The banderklown has advantage on attack rolls against any creature it has surprised.

False Appearance. While fully withdrawn into its shell, the banderklown is indistinguishable from a Small jack-in-the-box toy.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage, and if the target is a Medium or smaller creature, it must succeed on a DC 13 Dexterity saving throw or be swallowed by the banderklown.  A swallowed creature is blinded and restrained, it has total cover against attacks and other effects outside the banderklown, and it takes 10 (3d6) necrotic damage at the start of each of the banderklown’s turns. A creature reduced to 0 hit points in this way stops taking the necrotic damage and becomes stable.

The banderklown can have up to three Medium or smaller creatures swallowed at a time. While the banderklown isn’t incapacitated, it can regurgitate any swallowed creature at any time (no action required) in a space within 5 feet of it. The creature exits prone.  If the banderklown dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 5 feet of movement, exiting prone.

Shell Defense. The banderklown withdraws into its shell. Until it emerges, it gains a +4 bonus to AC and has advantage on Strength and Constitution saving throws. While in its shell, the banderklown's speed is 0 and can’t increase, it has disadvantage on Dexterity saving throws, it can’t take reactions, and the only action it can take is a bonus action to emerge.