Lammasu

Lammasu is a bizarre creature type with the body of a cow, a bird's wings and a human face with horns, based on the Mesopotamian creatures of the same name (and appearance). So far, two lammasu have been printed, both associated with white mana.

Ravnica
Ravnican lammasu once ruled the velds of the plane before the arrival of the urban sprawl. Only a few remain alive today, flying in its skies while being hunted by horrors. Since these are only represented by the Ravnica: City of Guilds card Hunted Lammasu, and do not feature in Return to Ravnica, it is most likely that they are completely extinct.

Tarkir
Tarkir Venerable Lammasu are enigmatic nomads, soaring high above the land across all seasons. None know of their true purpose, but they arrive frequently in turning points of history.