TY: Level 4 (average die-rank: D8)
TR: Melee: Slam -- 1D4 + 4 (acid damage)
Arcana: D12 + D8 (Paralyze)
Notes: Gelatinous cubes secrete acid that dissolves organic material, but does not affect metal or stone. Any creature that is struck by a gelatinous cube receives paralysis damage to Resilience. Creatures reduced to 0 Resilience as a result of a paralysis attack become paralyzed (a saving roll against Endurance is allowed each round). If a gelatinous cube engulfs a creature, the victim takes maximum damage each round.
Again, not the standard use of Arcana, but I think this is a good way to model the "if it hits, it causes 'X' effect which requires a saving throw" type of creature. Thoughts?
I like your adaptation of level into type, that's cool, and it works with the system. The D12+8 threat points reducing Resilience, and then paralysis occurring works too! It breaks no rules.
In fact I bet you could create any monster without regard to a single "formula" in the book and would still find it tough to "break" anything.
No how about what happens after the cube gets to envelop the victim? Like 1D10 damage straight to toughness per round...