Board Thread:General Discussion/@comment-26133480-20170712023633/@comment-27089028-20170718103548

If Mettaton were human his soul would be used to help break the barrier and would be much stronger plus only he would have needed to be absorbed by Flowey for the latter to become Hyperdeath Asriel as it would meet the human soul requirement. The fact is Mettaton is not a human but a Monster same as his cousin Napstablook.