Rust Bat

Small monstrosity, neutral

Armor Class 13 (chain shirt) or 15 (half plate)
Hit Points 5 (1d6+1)
Speed 5 ft., fly 40 ft.

11 (+0) 15 (+2) 13 (+1) 2 (–4) 12 (+1) 4 (–3)

Damage Immunities nonmagical weapons, cold, poison, holy water
Senses darkvision 60 ft., passive Perception 11
Languages none
Challenge 1/4 (50 XP)


  • Iron Scent. A rust bat can smell ferrous metal within 30 feet.
  • Corrosive. Any non-magical metal weapon used to hit the Rust Bat immediately corrodes with rust. Each time a weapon hits, after calculating damage, the weapon’s damage rolls are permanently given a -1 penalty. If this penalty drops to -5, the weapon becomes useless.
  • Natural Camouflage. Rust bats have advantage on Dexterity (Stealth) checks made to camouflage themselves against rusted metal.


  • Swoop. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: The Rust Bat attaches to metal armor or a metal, causing it to have a cumulative -1 penalty to the AC it offers with each hit. The bat can also target a held metal weapon, causing it to rust as described under the Corrosive trait above.

Rust bats, also called rynocks, are about two feet in length. They are red-brown in color with underbellies of burnt orange. Rynocks feed of ferrous metal. They attack by swooping down and attaching to their prey.

Looking for the largest metal objects to consume, rust bats will typically target armor, shields, and weapons, in that order. Rynocks hang from ceilings like other bats, but also will use their natural camouflage and attach themselves to rusted metal to surprise their prey.

Section 15: Copyright Notice

Dwarrowdeep 5E, Copyright 2022; Greg Gillespie.

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