Lost in the sauce, overwhelming power, a thirst for revenge-

A dormant curse woke up the in the desert, making a sweet boy to a beast dishing punishment. Essau realized he could be a sand beast, a savage spirit his parents told him about in tales and legends of his folklore, quite a surprise 'w'

Essau belongs to me, the sand beast was also made to have a beast/monster/feral-ish version for Essau
And yes, the shape is from the skeleton of a Tigrex (though friend told me it was a Nargacuga/Barioth ahah)