Combustion Cube
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The Combustion Cube, the Slow Furnace
Notebook of a siege mage
What it is
Like all gelatinous cubes, it is a golem: it is made, given an order, and it carries that order out. But the combustion cube knows only one, to destroy. No mage, however skilled, keeps one in a dwelling or a city, for it would end up reducing everything there to ashes. That is why it is one of the few cubes used as a weapon, released into a besieged fortress or into tunnels someone wants emptied of all life.Appearance
You catch sight of it. Around the bend of a dark corridor, a red glow pierces the gloom, followed by the smell of soot. The air turns heavy and dry, and the heat reaches you long before the light.It draws near. Everything that passes close to it bursts into flame. Within its body, glowing like an ember, crimson remains are still being consumed, and you understand that with this one, death comes far faster than with the others of its kind.Combat
How it fights. Slow like all cubes, it has no need to touch you to do you harm. Its heat is magical and spreads through anything that conducts it: metal becomes a stewpot in which you cook alive, cloth catches fire, and only leather holds up reasonably well. On contact, the pain becomes unbearable, and you must still fight the pull dragging you toward its center.How to fight it. Avoiding it is still best: it is slow, and a closed door buys time. If you must face it, ice magic wounds it cruelly. But never water: it instantly turns into scalding steam, which does nothing to the cube and scalds you instead.
A token or encounter asset depicting a gelatinous cube variant engulfed in fire, with a skeleton and miscellaneous debris visible within its translucent red body, set in a stone corridor with arched architecture. Known as the Combustion Cube, this creature functions as a siege weapon or dungeon hazard, releasing radiant heat that ignites flammable materials and superheats metal armor without requiring direct contact. Suited for combat encounters in dungeons, fortresses, tunnels, or siege scenarios, it is compatible with fantasy RPG systems such as D&D 5e, Pathfinder, and OSR, and works as a token or scene element on virtual tabletops including Roll20, Foundry VTT, and Fantasy Grounds.
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