Carriage of Ice Ravens

Keen Perception. The carriage has advantage on Wisdom (Perception) checks that rely on hearing and sight. 

Swarm. The carriage is like a swarm and can occupy another creature’s space and vice versa, when the swarm does so that creature rides in the carriage as if it was a mount. The carriage can’t regain hit points or gain temporary hit points.

Peck. Melee Weapon Attack: +7 to hit, reach 0ft., one creature in the carriage's space. Hit: 9 (3d6) piercing damage, plus an additional 4 (2d4) cold damage or Hit: 6  (2d6) piercing, and 4 (2d4) cold damage damage if the swarm has half of its hit points or fewer,  

Frozen presence. When occupying another creatures space the summoner deems an enemy, at the start of the creatures turn they take 8 (4d4) cold damage, the creature then must make a DC 15 constitution saving throw, on a failed save the creature is frozen till the start of their next turn, and on a success the creature is not frozen