Hey, so I was about to do a "Kill all Enemies" run, but I only found 20 out of 21 enemies. Where is the last one?

So far I found: Tutorial - Enemy 1, 2 Ice Area - Boss and Enemy 3 Grey Area - Enemy 4 Green Center - Enemy 5 Poison Area - Boss and Enemy 6 Grass Area - Enemy 7, 8 and 9 Small Desert - Enemy 10, 11 and 12 Small Area below the desert - Enemy 13 "Town" - Enemy 14 Big Desert - Enemy 15, 16 and 17 Final Boss Area - Boss and Enemy 18, 19 and 20

I searched through all the areas but I still can't find it. Where is the enemy 21?