Board Thread:General Discussion/@comment-27174095-20160117010358/@comment-27490087-20160128032907

Ethanlac wrote: Doing a Genocide run locks you out of the other endings, FYI. But it does come with the two hardest bosses. So there is that drawback to it. It does? I thought it just changes them to be more... bad ending-y.

Even then, you can uninstall and reinstall the game, or delete the flag that makes the endings change after you do the Genocide route in the game files.