Soltan's form comes with a price. Since he's only part Sombra, he needs to "recharge" his magic once a month or this happens. His body loses control over the shadow parts of him, and his weight balloons out to one section.

The weight and shadows move and spread over his body as he waits to recharge, the fat flowing like a lava lamp from top to bottom, very slowly. The shadows like water and changing whatever section they're currently covering into Soltan (mostly just the coloring) while the rest of his body is Zoltan.

To recharge he has to use the magic ring Shippo gave to him, made from his old pendant. He wears it a few days a month to absorb its limitless energy and then he pops back into Soltan form fully.