Undead : Devil

Undead : Devil swaps the crucifix of its parent for a tiny demon, and it costs far more. The Sol's RNG Wiki lists it as a Legendary mutation of Undead added in Era 2, with a breakthrough chance of 1 in 666,666 and a native chance of 1 in 111,111 inside Hell. At 10x luck that is about 66,700 rolls in the open or 11,100 in Hell, a long grind but much shorter than the nine-digit auras in the same biome.

It was drawn by djkustomsr from a concept by 53_Axis. Visually, there is no cross at all: the player gains red glowing wings, horns and a triangle-tipped tail while a large red portal swirls underneath. A faint hex-style pattern hangs in the air, and the character hovers off the ground, bobbing slightly as the wings and tail move together. The wiki notes its cutscene begins like Undead's, with the same drop-beat sound and a star at the center, before the red theme takes over.

The in-game text is just two words calling it the tiny demon.