Board Thread:Questions and Answers/@comment-26245394-20160809211449/@comment-27701762-20160809211958

The "1 left" is just a random encounter. Find an area where there are random encounters, then hold Up+Down. After a bit (the time you need to wait is variable, though it may take a minute or two at least), you should come across a random encounter. Kill one enemy, and you should be done.