Easter eggs from Metroid series have appeared in some games created by Nintendo. Some appeared in Mario games, some appeared in Kirby games, and some appeared in Wario games. They rarely occur in Yoshi games.
In Super Mario RPG: Legend of the Seven Stars, Samus Aran will appear in the one of the rooms in Toadstool’s Castle in the Mushroom Kingdom if you help Mario manage to obtain six out of seven stars during the quest to restore the Star Realm. Also, Samus Aran’s Gunship appears as a small figure in the Shop Hall within Barrel Volcano while Mario tries to obtain the sixth star nearly taken away by the Axem Rangers. In Mario & Luigi: Superstar Sage, one of the items that was supposed to be given from Samus Aran is actually given to the Mario Bros. by Professor E. Gadd for having to let him sample of the coffee items created with sufficient amount of flavored beans found in the Beanbean Kingdom. One of the music pieces in the Metroid Prime: Federation Force played by Amadeus Wolfgeist in Luigi’s Mansion 3 is heard before Luigi tries to fight him. The Space Pirate also appears in the framed poster in the Entrance Hall of Paranormal Productions.
In Kirby’s Dream Land 3, there is a level where Samus Aran appears as an Easter egg at the end before the goal. If Kirby is able to defeat all Metroids by using the ice copy ability, Samus will reveal her human face and reward Kirby with a Heart. One of the items from the Metroid series, the Screw Ball, appears as an Easter Egg treasure item in The Great Cave Offensive in Kirby Super Star.
In Yoshi’s Wooly World, scanning the Samus Aran amiibo will unlock a yarn-developed Yoshi resembling Samus Aran.
In Wario Land 2, a Metroid appears as a Metroid Easter Egg treasure that can be obtained in the minigame found in a specifc level.
In Animal Crossing games excluding New Horizons, furnitures and clothing belonging to the Metroid series appear as Easter Eggs. One of the Metroid music tingles occur in Animal Crossing: New Leaf if you try on the Samus clothing. The Samus clothing along with the Metroid furniture can be obtained via the correct corresponding fortune number from Fortune cookies. Interacting with the Metroid furniture will trigger a creepy music piece from the Metroid series.