Ymir

Ymir appeared in 1957 movie called 20 Million Miles to Earth. The Ymir was a green colored scaly alien, with a dinosaur-like tail, feet with a humanoid upper torso and arms, along with a sagittal crest on its head. It also had simian-like facial features with large jowls hanging from its cheeks. It constantly increased in size due to tissue build-up as a side effect of inhaling Earth's different atmosphere from its own native world. At the time of it's death, it stood somewhere between 10 to 20 feet tall. The Ymir was a gentle creature, until it was locked in a cage for a whole day, later to be assaulted by a farmer and his dog, which turned it into a malevolent and aggressive monster. The once-peaceful beast became hostile with both humans and animals alike after the incident and attacked them without second thought. Then it was chained down by the US air force upon capture, and shocked with an electric cage to paralyze it. Upon being donated to the Rome zoo for research, it eventually broke free and was now more agitated than ever. The constantly growing Ymir was on a rampage in Rome, where the creature was finally put out of misery by the military's firearms and vehicles, serving as a reminder of mankind's own cruelty and ignorance.