The gila monster is a monster added in SLASH'EM.
Despite its name, it's a real animal, the encyclopedia entry is exact. It's a species of lizards in the south west of the US. It really has a venomous bite.
[Gila monsters] are stout-bodied lizards with short legs and a short,
fat tail. They're covered with bright irregular markings, usually
pink, yellow or white, against black or brown scales. They are shy,
retiring creatures unless they're provoked. Then they can be
dangerous because they secrete a neurotoxin -- a poison that
destroys nerve tissue -- from their salivary glands. In humans,
their bite can result in severe pain and even death.