OoPAs - Out of Place Animals

OoPAs (short for Out of Place Animals) are strange beasts that have begun wandering the Underdark in recent years. No one is quite sure where these strange creatures are coming from and the harsh Underdark has a sore lack of ecologists that could investigate such a matter.
These creatures are largely predatory, which allows them to fit into the Underdark's environment well. Most resemble conventional beasts with some type of strange, additional anatomy that causes most who encounter them (and live to tell the tale) to regard them as monstrosities instead.
Despite having appearances resembling natural creatures, the body of a slain OoPA will quickly start to fade away moments after death. This process bares resemblance to similar phenomenon that occur with otherworldly creatures who return to their home plane upon "dying" in another realm, such as fiends or celestials. As such, many Underdark residents have concluded that these strange creatures are from another plane; there is just no consensus on which one.
The dissolution of an OoPA corpse is more complete than other otherworldly creatures, leaving behind no remains whatsoever under normal circumstances. The sole exceptions are body parts removed from an OoPA using Gobo's Dimensional Ripper. Gobo himself is the only known person who can make use of these monster parts, turning them into equipment-enhancing magical trinkets using "ancient goblin secrets" (or so he calls his mysterious crafting techniques).

Known Types of OoPAs

• Armadillo - Encountered as the party entered the Underdark. Killed by Sunny. Paralysis sac and x2 carapaces harvested by Jake.
• Frog - Encountered at Glogdolp during Nogah's attempted religious uprising. Killed by Leh'ct. Inflation sac, muscle, and flotation sac harvested by Jake.
• Ostrich - Encounter and killed by Ban as he was catching up to the Thaig Expedition. Beak, ear, and feather harvested.
• Spider - Encountered as the party crossed the Silken Paths. Killed by K. Spike, claw, and piece of hide harvested by Leh'ct.

Related
Gobo's Trinkets