Black Spitter Gecko (5e Creature)
From D&D Wiki
Tiny beast, unaligned
Spray. Ranged Weapon Attack: +5 to hit, range 5/15 ft., one target. Hit: 2 (1d4) acid damage.
Black spitters are small geckos that have adapted to their position as prey by developing an acidic defense. These tiny creatures are most prized by rogues and thieves as pets as their saliva is known to be able to corrode iron. With enough time — or enough black spitters, a finely crafted lock or mechanism can be reduced to little more than rust.