Ethereal Cube

This monster came into being during a game. The party was trying to trap an unknown monster, patrolling the city invisibly at night. A thief tried to mug the one PC who was visible, and was beaten unconscious for his trouble. The party decided to use him as bait, to see if it would attract a monster.

If turned over to the city guard, it was likely the thief would be executed, so in using him as bait they gave him a chance at survival, and in any case, he’d do at least one useful thing in his life. Even if he didn’t intend it.

As DM I know the monster they were trying to find would not be attracted, but decided to have fun with it. The thief became hazy, then faded from sight, leaving an acidic residue that evaporated in minutes.

At that time I created an effect for fun. Later I developed this monster to explain the situation.

Ethereal Cube

Frequency very rare
No. Encountered 1
Size L (5′ to 10′ cube)
Move 120 feet
Armour Class 6
Hit Dice 4 to 8
Attacks special
Damage 3d4
Special Attacks paralyzation, surprise
Special Defences see below
Magic Resistance standard
Lair Probability 0%
Intelligence Non-
Alignment Neutral

Ethereal cubes are a type of gelatinous cube, essentially large garbage cleaners that consume virtually any organic matter. As the name indicates, they are encountered primarily on the Ethereal Plane – these monstrosities wander the plane sweeping up organic matter and digesting it. Note that they are indiscriminate in what they ingest – everything in their path, including dirt and rocks, may be swept up. Non-digestible items will be disgorged every 4d4+4 turns, leaving a small pile of objects devoid of anything organic.

The flesh is nearly transparent. In bright light they are clearly visible but may surprise characters 1-3 in 6 due to the silent and relatively rapid movement. In darker conditions they easily surprise creatures on a roll of 1-5 in 6 because of their near invisibility. Note that inorganic objects suspended within the creature may reduce this surprise ability (at the DM’s discretion).

Any creature touching the beast with bare flesh suffers 3d4 hp of acid damage and must save vs. paralyzation or be paralyzed for 6d4 rounds. Open hand attacks are ill-advised for this reason. A cube may normally attack only one creature each round, pressing it’s acidic flesh against its victim, but in some circumstances the cube may be able to attack more opponents (at the DM’s discretion).

Paralyzed characters will be enveloped by the cube – it glides forward around them. Globules of clear acid inside the creature shift to dissolve the victim(s) at a rate of 3d4 hp/round. Humans, demi-humans, and most goblinoids will typically be killed within a few rounds, and the soft flesh dissolved within a further 3d6 rounds, leaving a cleaned skeleton. Unless the cube disgorges the skeleton it will be dissolved within a further 3d6 turns.

Note that this affects only organic matter – metal objects are typically unaffected, although oxides such as rust are absorbed, effectively shining metals such as steel and silver.

On the Ethereal Plane they may be struck by normal weapons, although organic weapons (e.g., wooden clubs) must save vs. acid on each blow or dissolve in 1d4+1 rounds. Enchanted items get a bonus +1 and “plused items” also get the item’s plus as a bonus, e.g., a Club +2 get a total of +3 on the saving throw.

When reduced to zero hp or less, the binding force that holds the cube in its shape is lost, and the creature “melts” in 1d3 rounds. The resulting liquid is highly acidic and inflicts 2d4 hp of damage per round against all organic matter it touches. Oddly enough the liquid dissipates in 2d4+2 rounds, leaving no trace. Due to these factors it is suspected that cubes are the result of magical experimentation, but no effort to recreate them has succeeded.

Cubes may sense large quantities of organic matter, preferably flesh, within 100 yards, and will travel towards it. While evidence indicates the cube prefers non-living flesh, it may attack living creatures.

Ethereal cubes have a very deadly ability. Once per day they may briefly shift to the Prime Material Plane. The transference requires 1 round to accomplish, the cube remains on the PMP for 1 round, and then a third round is required to shift back. While on the PMP the cube may be struck with normal weapons, but during the two rounds of shifting a +1 or better weapon is required to hit them.

Studies have evinced the idea that cubes will transfer to the PMP if they sense a dead or badly injured creature adjacent on the PMP. It will shift planes, envelop the creature, and shift back, leaving a square patch free of all materials and a glistening residue where the creature was. The glistening area is acid which will inflict 1d4 hp of damage to any creature touching it. The acid dissipates in 1d3 rounds, leaving no trace.

Cubes are subject to damage from fire, but are immune to acid, electricity, mental attacks, illusion, paralyzation, poison, sleep, and holds. Cold causes no damage but if the cube fails a save vs. spells it will be slowed for 3d4 rounds and will disgorge all contents the round following the attack.

A cube will gain 1 hp for every 8 hp it digests, and for every 8 hp gained it will grow 1 HD. This continues until it reaches 9 HD, at which point it divides into two 4 HD cubes of half size. If this happens in battle the creature will be unable to attack during the round of division, but its foes will face two enemies the following round.

DM Note: regardless of current hp, roll fresh hp for the divided monsters.


Ethereal cubes are mindless and collect no treasure. However, they leave behind clumps of inorganic matter, which may include items that are valuable to sentient beings. They may also have inorganic material suspended inside them.

Level/XP Value

Hit Dice AD&D 5% Rule

I haven’t calculated XP as yet

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