Might need a little tweaking, but I'm throwing a pack/flock/whatever of these guys at my players this weekend...
VOLT
Small aberration, unaligned
Armor Class 14 (natural armor)
Hit Points 13 (3d6 + 3)
Speed 10 ft., fly 30 ft.
Str 8 (-1) Dex 17 (+3) Con 12 (+1)
Int 2 (-4) Wis 10 (+0) Cha 6 (-2)
Damage Immunities lightning
Senses darkvision 60 ft., passive Perception 10
Languages ---
Challenge 1/2 (100 XP)
ACTIONS
Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) piercing damage, and the volt attaches to the target. While attached, the volt doesn't attack with it's bite. Instead, at the start of each of its turns, the target loses 5 (1d4 + 3) hit points due to blood loss.
A creature, including the target, can use its action to make a DC 10 Strength check to detach the volt.
Tail Slap. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) lightning damage. Against an attached target, the volt gains advantage on its tail slap attack roll.
(Originally appeared in the 1E Fiend Folio)
From what I can tell, this monster is overpowered for a third level monster.
1) AC is about 2 too high for a 3rd level monster. Not too bad if the creature is not attached, but it should be lower if it is attached.
2) The bite attack auto-damages in latter rounds if the creature is not detached (this is stronger than an advantaged attack).
3) Since PCs will sometimes try to detach the creature to stop the auto-damage, it means that they are not attacking it. A negative action economy issue. You hit me, I pull you off. You hit me, I pull you off. If the creature is not killed immediately by the PC (or a friend), then the creature (more or less) damages every single round until slain (yes, it could get pulled off and miss, but the effort to pull it off might miss instead).
4) The damage done by the tail is fairly strong, even if the creature does not have advantage. Course, both the bite and the tail cannot be done in the same turn unless it is attached.
5) And a creature that can fly has an innate advantage. It should be able to swoop down, hit with the tail, and then swoop away, limiting responses to ranged attacks.
As a comparison, a 5th level Next brown bear had an AC of 10 and two +5 attacks, one that averages 7 damage and one that averages 11. This creature has the same +5 to hit, an AC of 14, can fly, averages 5 with one attack and 10 with the other (both attacks which could sometimes get either autohit or advantage). Granted, this creature has low hit points, but that is the only weakness it has. It still takes about 2 solid hits to kill it.
5 of these 3rd level volts against 5 3rd level PCs should easily result in a lot of damage taken by the PCs. It would be a really nasty encounter for same level foes and should suck down quite a few of the PC's hit dice for the day.
