Wherein your humble scribe presents a new monster for Swords & Wizardry (Core Rules), the Pyroceros.
A Pyroceros looks much like a normal rhinoceros, except that its horn is composed of a powerful, ever-burning magical blue flame. Strikes by this horn have a 50% chance of igniting any flammable material worn by the unlucky victim. Characters wearing or holding an ignited item will suffer an additional 1d6 damage from the burning for 1d4 rounds or until they rid themselves of the burning material.
Pyroceros: HD 9; AC 4 ; Atk 1 flame horn (3d6) or 2 trample (2d4/2d4); Move 12; Save 6; CL/XP 11/1700; Special: only take half damage from fire-based attacks, burning damage continues after successful horn attack.