EXTRA: Pako BattiliarG 5

As the description suggests, this requires you to kill 161616 of the bat enemy. This unlocks retroactively meaning if you’ve already killed the required amount, it’ll unlock at the end of the first level you play.

If you need help finding bats, they’re extremely common in both Mad Forest (the first level) and Bat Country (unlocked by reaching level 80 in Inverse Mad Forest).