Fun fact, the Coeurl originally comes from the short story Black Destroyer.

It was the inspiration for the Displacer Beast too - I read that story in 7th grade, I felt so bad for that purple-eyed tentacle kitten

Heh, we always sympathize more with the monsters than the heroes, don't we? I cried at the end of 20 Million Miles to Earth, for example, and Eugène Lourié's daughter was very upset by the ending of The Beast from 20,000 Fathoms (or was it The Giant Behemoth?); "Daddy, why did you kill the nice beast?" she demanded. Lourié was the director, and his daughter's reaction is apparently what inspired him to have Gorgo end with the monster and his mom surviving and walking away after she frees him from the circus.

In Black Destroyer, I was struck by how hopeless and tragic Coeurl was in his own way. The last of his kind, stuck on a dead world... and then along comes Commander Morton's expedition. The way the plot unfolds as he gains and then betrays the astronauts' trust in order to kill them and steal their ship reminds me of the way Rob, a monster who disguises himself as a human, explains his actions in the X-Files episode Hungry. At the end, after he comes to the tragic end awaiting most sympathetic monsters, he tells his psychiatrist Dr. Rinehart as he lies dying that "I can't be something I'm not."

The best monsters are the tragic ones. Humans label that which is different and, yes, often dangerous, "monster" and destroy it.