Both cards are the first Structure Deck Exclusive cards to be in two different Structure Decks.
Cerberus was the three headed dog of the underworld in Greek mythology. However, this depiction is inaccurate since the card pictured has two heads instead of three (though depending on the story, Cerberus could have as little as one head or as many as 50). Cerberus also had a brother named Orthrus which was a two-headed dog that guarded Geryon's sacred cattle.
The fact that this monster's heads are from different animals also makes it similar to the mythological Chimera.