Board Thread:Questions and Answers/@comment-29496956-20161230151848/@comment-27701762-20161230153403

No, you are not technically required to kill each and every monster you encounter. You simply need to kill enough enemies to satisfy the criteria in each area. The only exception to this is Snowdrake, which you must kill in order to progress with the Genocide Route. Sparing or running away from Jerry will not abandon your playthrough.