Kirby

Kirby is the main and titular character of the Kirby franchise. Like Samus Aran, he is a playable fighter in every Super Smash Bros. title.

Kirby franchise
In Kirby Super Star, if Kirby uses his Stone ability, there is a slight chance of him transforming into a statue of Samus Aran.

In Kirby's Dream Land 3, specifically the second stage of Iceberg, Kirby can encounter Samus Aran and six Metroid larvae, and Samus will appear unmasked and give him a Heart Star or 1-up if Kirby destroys the Metroids with the Ice ability. Interestingly, the Metroids cannot harm Kirby, even if they latch onto him and try to feed.

Super Smash Bros. series
In both the Kirby and the Super Smash Bros. games, Kirby has the ability to swallow enemies and copy their abilities. If he swallows Samus, he will wear her helmet and be able to use the Charge Beam. If he swallows Zero Suit Samus, he will have her ponytail and be able to use the Paralyzer. In Ultimate, if he swallows Ridley, he copies his fireball move and wears a hat based on Ridley's head. Similarly, he wears Dark Samus's "helmet" if he swallows her.

In Zero Suit Samus's gameplay trailer for Ultimate, Kirby alongside Sheik fight Zero Suit Samus on the Big Battlefield stage, but she manages to deliver repeated blows to them both before knocking them both out of the stage. In the gameplay portion of the A Piercing Screech trailer for Ultimate, Kirby fires his Charge Beam while using her helmet on the Mushroom Kingdom U stage before turning around to face Ridley just as he arrives and uses his down Taunt. In Dark Samus's reveal trailer for Ultimate, at the Lylat Cruise stage, both Kirby and Dark Samus (with the former wearing a hat modeled after her "helmet") enter freefall with the latter curled up, and Kirby briefly spins.

Kirby, or rather his Keeby alternate costume, acts as a puppet fighter for the X Parasite spirit in the World of Light. This is most likely a reference to how both Kirby and the X Parasite have the similar ability of copying the abilities of anything they absorb.