Source: Tome of Horror Complete Sword & Wizardry. Originally from the AD&D 1e Fiend Folio.
The reclusive Lava Children generally makes their homes in burnt out volcanoes located in warmer climates. Their only friends tend to be only fire-themed creatures like magmin and fire elementals. These deranged looking child-like humanoids make great occupants of underground cities lost in time. Lava tubes snake through the underground leading the way to a tribe of Lava Children lost for centuries among the ruins.
They also make great minions for a stronger force like a genie. The Lava Children also work great as a civilization on a tropical island. Maybe a tribe of primitive humans has resorted to idol worship of the Lava Children. Associating the island lone volcano and it's activity with the demeanor of the Lava Children. The human tribe could be kidnapping people and sacrificing them to the Lava Gods...
The Lava Child signature ability is that metal objects has no effect on them. Lava Children simply ignore all metals from swords to armors. An encounter with a band of Lava Children can be a frustrating encounter for a melee heavy group.
Combat: The Lava Child has few interesting abilities. First any metal object that is used against a Lava Child simply passes through it. Also if a Lava Child attacks someone in metal armor it ignores that armor class bonus. They can also move through any solid metal surface as if they didn't exist. They are also immune to all earth spells. They are vulnerable to water and cold based spells.
- Lava Child: HD 4; AC 3 ; Atk 2 claws (1d4) and bite (1d6); Move 12; Save 13; AL N;
CL/XP 5/240; Special: Immunity to earth magic, fire and metal, double damage from cold