This is the opening theme for FrozenOver Stage 2 Phase 1. The reason why this character looks like this is that normally in other AU's, a monster can absorb a human's soul. However, in this case, it's the other way around. Deus somehow manages to absorb both Keith's and Sans's, souls. Even though this isn't technically possible, but Chara caused a few glitches that come into effect here before the Stage 1 fight even started. In phase 4 of that same stage, both Keith and Sans got struck down in relevance to the two soul capsules that were offered to Frisk/Chara. But, knowing that Frozentale Deus said something bad will happen if used at the wrong time, this is the consequence of abusing it. In response, the game actually crashed which is exactly Deus had warned Frisk/Chara about during their Pacifist run. They might have gone genocide first and didn't know about the warning. But by the time the game reloads back up, there were a few changes to Deus in response to trying to stop them in phase 4. Chara's usually the one behind it all, so he blamed them, knowing that Frisk won't go genocidal. Throughout this Stage 2 fight, Deus is determined to stop Chara, even though he lacked it in Frozentale.