Scimitar Oryx - The Desert Wanderer

The Scimitar Oryx is an Antelope mob that will be helpful to the player.

Spawning - The Scimitar Oryx spawns in the desert biome in groups of 3-5 and are a very rare mob to find in the desert biome

Behavior - The Scimitar Oryx are a neutral mob, and will only attack players if the players hit them, they will attack the players by using their horns. But these mobs can be helpful since they can lead players to desert temples, but in order for them to lead players to the temples players must feed them their favorite food, melon slices in order for them to lead players to desert temples but not only that, they could also trick the player and lead them out of the desert biome if a player doesn't give them the amount of melon slices they want. They are also breedable with wheat.

so there's my idea of a large desert mob.