A review copy of “The Cubonomicon” was provided by the publisher. Find more DMs Guild Reviews on my website and YouTube channel.

Support my work by using my affiliate links and pledging via Patreon.

Designed by: Micah WattElise CretelDrew DawesKerry JordanPaul Siegel

Do you like oozes? Really, really like oozes? The Cubonomoicon provides over 30 new variants of one of the most iconic monsters in Dungeons & Dragons, the Gelatinous Cube.

We’ve got portal cubes! Frigid cubes! Blinking shock cubes! Fiery cubes with big floating eyeballs inside! Cubes that transport mind flayers! Big ass cubes! And cute tiny cubes that can form a gargantuan cubepocalypse!

Have a thing against cubes? We’ve got other shapes as well, including bubbles, spheres,  pyramids, and even a bouncing dodecahedron!

For most of these new variants, The Cubonomicon takes the CR 2  Gelatinous Cube, with its blindsight , transparent form, and engulfing movement, and adds a single new trait or attack to spice things up.

The Mirror Cube can reflect spells, the Poison Cube inflicts the poisoned condition, the Pyramid can absorb and redirect spells, the Sphere can quickly surge forward, and the Spitting Cube can spit acid. Using these modified variants is a wonderful response to metagaming (whether intention or not), especially if you can telegraph how different these new variants look.

Thankfully each creature includes a lovely piece of original artwork that shows off the colorful variety of oozes, with a healthy dose of humor. I’m also a big fan of the slimy layout that encircles each page.

blue fire cube

Several of the more interesting oozes create challenging new situations for players, or introduce entirely new ooze symbiotes.  The Binary Cubes are divided between a mouth and stomach cube, with an engulfed victim teleporting up to 500 feet into the other cube! The Shock Sphere can deal lightning damage in water, while the Memory Cube changes its pseudopod attack to whatever damage it most recently received.

The Cube Thrall is controlled by a mind flayer that safely pilots it like vehicle from within — tell me that isn’t a memorable sight! And just imagine the look of grinning horror after unleashing the Incredible Shrinking Cube on a party after it shrinks and escapes with its first victim. Delicious.

Cubes range from CR 1/8 up to CR 20, with the aptly named Gelatinous Cubepocalypse Swarm at the top of the pack, siphoning off swarms of Cubelets while engulfing enemies and reconstituting itself.

Since CR 2 is relatively low tier, one of the common themes is “Gelatinous Cube but harder,” which would describe over 20 of the variants. One of my personal favorites is the CR 9 Venus Slime Trap, a combination Roper and Gelatinous Cube that reels in victims to be engulfed while it sticks to the ceiling.

My only complaint is that some of the variant statblocks don’t quite reflect the interesting concepts from their descriptions, and too often fall back on the standard Gelatinous Cube traits. For example, the Mirror Cube reflects all images on its surface. Why not change its standard engulf into a WIS save that forces victims who see their reflection to walk willingly into the cube?

Likewise, Hadar’s Cube is born of a collapse Hunger of Hadar spell, yet all it gains are tentacle attacks. Surely anything it consumes would be displaced into a pocket dimension where victims suffer psychic damage, or perhaps inflicted with madness?

I’m not even the biggest fan of oozes, but I’m incredibly impressed with the variety and creative application of traits, features, and attacks that expand upon everyone’s favorite ooze.


  • Over 30 new varieties of Gelatinous Cubes and related oozes, ranging from CR 1/8 to CR 20.
  • Creative ooze variants that include different shapes, sizes, spells, and creature hosts.
  • Delightfully slimy design and original artwork for every ooze.


  • Some of the statblocks aren’t as interesting as their concepts.

The Verdict: the Cubonomicon offers over 30 clever and creative varieties of Gelatinous Cubes, creating a gold standard for monster variant books and a must-have for ooze lovers.

A review copy of “The Cubonomicon” was provided by the publisher. Find more DMs Guild Reviews on my website and YouTube channel.

Support my work by using my affiliate links and pledging via Patreon.