Emanate Shadow. Always present. The shadow stirge is cloaked in shadow encompassing all adjacent spaces five feet from it. Any spaces which are brightly lit become dimly lit. Any spaces which were dimly lit become darkness. This shadow is magical in origin but is weak. Darkvision and normal light sources behave normally with it. Dim light or darkness may present conditions on skill checks and attack rolls respectively.

Cloak of Shadow. If the shadow stirge has not moved during its turn it may use its action to hide with +4 to its Stealth check. 

Blood Drain. Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 5 (1d4 + 3) piercing damage, and the stirge attaches to the target. While attached, the stirge doesn't attack. Instead, at the start of each of the stirge's turns, the target loses 5 (1d4 + 3) hit points due to blood loss.

The stirge 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 stirge.