Coffin Crawler

The crawler has advantage on saving throws against being charmed, and magic can't put the coffin crawler to sleep.

Coffin's Curse. Whenever crawler hits a creature with its bite attack, that creature is forced to remain in its current plane until the curse is removed by the remove curse spell or other magic. 

Relentless Tracker. The crawler knows the distance to and direction of any creature under the effect of its curse, as long as the creature and the crawler are on the same plane of existence. If the creature being tracked, the crawler knows.

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

Sunlight Sensitivity. While in sunlight, the crawler has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Web Walker. The crawler ignores movement restrictions caused by webbing.

Multiattack. The coffin crawler makes three attacks, either with its longsword or its longbow. It can replace one of those attacks with a bite attack.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 2 (1d4) piercing damage plus 9 (2d8) poison damage.

Leg slash. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) slashing damage.

Spit Dart. Ranged Weapon Attack: +6 to hit, range 150/600 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 4 (1d8) poison damage.