Read-only feature:

Get Aeon Reserve Tank (refills gauge when empty) / After beating game: Unlock Metroid II art


Read-only feature:

Place a Metroid Marker (see closest Metroid on map) / After beating game: Unlock Fusion difficulty mode and play with Fusion suit


Read-only feature:

Get Missile Reserve Tank (replenishes missiles when empty) / After beating game: Unlock concept art


Read-only feature:

Get Energy Reserve Tank (replenishes health when empty) / After beating game: Unlock Sound Test mode