At the Theros world-building panel at PAX, much was said about monsters, as they are a key element of the Theros flavor. One famous monster from Greek mythology is Cerberus, the three-headed dog who guards the underworld. Of course, one of the mythics in Theros is already a representation of that character, but the panel went on to show that Cerberus is considered a species on Theros, and then gave another, much smaller, example. Here's Two-Headed Cerberus:
Two-Headed Cerberus 1RR
Creature - Hound (Common)
Double strike (This creature deals both first-strike and regular combat damage.)
The left head keeps the right head starved as motivation to track new prey.
Technically, a two-headed Cerberus would be called an Orthrus - Echidna and Typhon did have a son who was a bicranial dog-monster - but insisting upon this point would be the equivalent of outing yourself as a huge dork. Still, there's a remarkable lack of double strike creatures flavored as literally having two heads, and this is simple, effective, and resonant as a common should be. It's also probably going to be very good in Limited, given the amount of pump effects that will no doubt be in Theros?
What do you think of this smallish Cerberus? Let me know in the comments.