How many bodies does Yuma Kuga have?
Yes, he indeed has three bodies, but nonetheless he only has access to two of them at any time.


Yuma's fleshly body is safely stored in suspended animation inside the black trigger ring his father created. Inside the ring, time passes ever so slowly that Yuma's certainly fatal wounds have not yet killed him even three years after the incident. This body is black-haired.
The "civilian" trion body. The one he uses whenever a trigger is not active. This body is made of Trion (see the scene in ep.2 when he is run over by a car, leaving only a small crack on his face). This body supposedly requires nutrients (since Yuma is shown to be eating). It has white hair.
The trion combat body, that replaces the civilian body (or is morphed into) when Yuma goes "trigger on". During the fight with Miwa squad in the abandoned train station, this body has an arm cut off. When Yuma "trigger off", the combat body is dissolved and the intact civilian body is replaced.
 3.1 Also during his fight with Viza in ep. 34, Viza successfully kills Yuma combat trion body, and his black trigger restores the civilian body. Being made of Trion, Yuma uses the inertia of his movement and a seal to burst through Viza's combat body. Viza is seen remarkably surprised for all his combat experience.


It is supposed(whom?) that if and when Yuma is able to heal his flesh body, the black ring will stop mantaining the trion civilian body.