Starfy

Starfy is the main character and the hero of The Legendary Starfy series, known as Densetsu no Starfy in Japan. Prior to the series' international debut of the Nintendo DS game, The Legendary Starfy, he was referred to by his Japanese name Stafy in English media.

Densetsu no Starfy 3
In Densetsu no Starfy 3, Wario makes a cameo appearance where helps Starfy throughout the Undersea Ruins by using some of his transformations from Wario Land 4. Wario and Starfy arrive at a vortex, where they must enter to locate the switch and four Jewel Pieces in order to unlock the boss door. Wario can transform into Bubble Wario, Flaming Wario and Puffy Wario, respectively. Upon completing levels, the player receives four different treasures - a Wario Cap, a Wario nose/mustache set, a copy of WarioWare, Inc. with a Game Boy Advance, and a pile of treasure.

Densetsu no Starfy (Yumiko Sudō) manga
Wario appears in the eighth chapter of volume two of the Densetsu no Starfy manga. This chapter is called Wario to Saikyou Tag da Fii! (Japanese: ワリオと最強タッグだフィー!), roughly meaning "With Wario, this is the Best Tag Team, Fii!". The chapter has Wario looking for treasure near a town in Starfy's world, before losing his treasure map, so Starfy and Moe decide to use Wario's treasure map to look for treasure and the map leads them to a cave containing the treasure, however, Moe gets separated from Starfy after Starfy accidentally activates a trap door.

When Wario comes (despite losing his treasure map), Wario and Starfy team up to find the treasure and they use the Wario Attack and Shooting Star ability to break a boulder blocking their way (which fell after Starfy activated the trap door) but it turns out that Moe had already found the treasure before them. When Wario and Starfy find Moe eating at a restaurant, they use the Wario Attack and Shooting Star ability against him.

Densetsu no Starfy 4
In Densetsu no Starfy 4, one of the collectable costumes for Starfy and his sister Starly (Stapy in Japan) is based on Princess Peach. Starly is also holding Perry, the parasol from Super Princess Peach. This costume is one of the winners of a costume designing contest held in Japan for fans.

Mario & Luigi: Superstar Saga
In Mario & Luigi: Superstar Saga, Starfy makes a cameo appearance on a movie poster in the Yoshi Theater, advertising a fictional movie called Legend of Stafy, using the Japanese pronunciation Stafy. This marks his debut outside Japan.

Super Princess Peach
In Super Princess Peach, a game also created by TOSE, Starfy makes a cameo as an enemy named Starfish. The Glossary even describes him as "A star-shaped foe rumored to be the prince of a kingdom?", which partly describes Starfy himself.

Super Mario Maker
Starfy appears in Super Mario Maker as a Mystery Mushroom costume, which can be unlocked by completing the "Starfy: Prince of Pufftop" Event Course.

Super Smash Bros. series
Stafy also appears in Super Smash Bros. Brawl, as an Assist Trophy character. However, unlike most Assist Trophies, Stafy is vulnerable to opposing attacks, and can be sent flying out of the stage easily. He makes up for this with strong attacks, as well as a wide range of moves, such as a spin attack, and a fiery explosion.

Starfy reappears in Super Smash Bros. for Nintendo 3DS / Wii U and Super Smash Bros. Ultimate with the same role and abilities.