Echolocation. The fleder can't use its blindsight while deafened.   Keen Hearing. The fleder has advantage on Wisdom (Perception) checks that rely on hearing.   Sunlight Sensitivity. While in sunlight, the fleder has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.   Undead Fortitude. If damage reduces the fleder to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is poison, radiant, or from a critical hit. On a success, the fleder drops to 1 hit point instead.   Spider Climb. The fleder can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.   Turn Resistance. The fleder has advantage on saving throws against any effect that turns undead.   Ambusher. The fleder has advantage on attack rolls against any creature it has surprised.   Surprise Attack. If the fleder surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 3 (1d6) damage from the attack.   Blood Frenzy. The fleder has advantage on melee attack rolls against any creature that doesn't have all its hit points.