The effect Yveltal had on Asriel's body was immediate--despite being fine earlier, he felt as though he hadn't slept in ages. He staggers and collapses on his knees, dizzy as he attempts to force himself back up. His inner Flowey hisses at him to get the hell out of dodge ("Unless getting incinerated again is what you want."), but his legs drag like iron balls and chains. He looks around for someone, anyone...

He had planned on retreating to the castle, but what with Yveltal plummeting there... so much for that.