Planeshift Tarkir
Blood Frenzy. The swarm has advantage on melee attack rolls against any creature that aren't undead or constructs that doesn't have all its hp. Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny insect. The swarm can't regain hp or gain temporary hp.
Blood Drain. Melee Weapon Attack: +4 to hit, reach 0 ft., one target in the swarm's space. Hit: 10 (4d4) piercing damage, or 5 (2d4) piercing damage if the swarm has half of its hit points or fewer, and the swarm attaches to the target. While attached, the swarm doesn't attack. Instead, at the start of each of the swarm's turns, the target loses 2 (1d4) hit points due to blood loss. The swarm can detach itself by spending 5 feet of its movement. It does so after it drains 10 hit points of blood from the target or the target dies. A creature, including the target, can use its action to detach the swarm.
Environment. Jungle, Swamp