Metroids appear in the second level of Iceberg. They can only be beaten with the Ice power (mirroring how Samus needs to use the Ice Beam/Missiles to defeat them). When you beat the level, Samus can be found standing in front of the exit. If you beat all the Metroids, Samus will have her helmet off. This a likely reference to the typical Metroid convention of allowing players to get a glimpse of Samus's face by getting a 100% collection rating.