Talk:Sans/In Battle/@comment-27792186-20160213213849/@comment-27810403-20160216162657

Did you make sure you stayed on the genocide route with the kill count and killing all the bosses? If the save point right before that doesn't pop up with the message "Determination." then you have moved back to the Neutral route.

Or you may have messed up the game files, but the explanation above is the only one if the files are still fine.