Cameos
Throughout the Mario series, many characters from other series made cameos. The large majority of these cameos are from characters developed by Shigeru Miyamoto and Nintendo. Some non-Nintendo characters have appeared as well, such as Sonic or Earthworm Jim.
Pikmin
Pikmin are a species of small plant-like creatures that exist in the Pikmin series. They have also appeared in the Marioverse on a number of occasions. Of the Pikmin that have appeared in the Mario series, only three varieties of Pikmin have appeared. Pikmin made their first appearance into the Marioverse during the events of Super Smash Bros. Melee. Pikmin can be collected as a trophy. A savegame of the Pikmin game is needed on the GameCube's Memory Card in order to get the Captain Olimar trophy.
Pikmin later made another cameo during the events of Mario Golf: Toadstool Tour. If certain flower beds were struck by a golf ball, Pikmin would pop out of the flowerbed and attempt to flee. These flower beds can be found in various stages. In WarioWare: Smooth Moves, Pikmin made an appearance in a Microgame.
Additionally, in the game Pikmin 2, a box of matches displaying Bowser's face can be obtained as a treasure. The game Super Mario 128 was also converted into what is now known as Pikmin as well. Additionally, Captain Olimar and his partner, Louie, are named after Mario (Olimar is an anagram of Mario, with an L added) and Luigi (Louie sounds like Luigi).
Captain Olimar is one of the most wanted characters for Super Smash Bros. Brawl, but it is unknown if he will be in it or not.
Earthworm Jim
Earthworm Jim is a mutated humanoid earthworm wielding a red ray-gun. Like Sonic the Hedgehog, it is believed that Earthworm Jim once entered the Marioverse. In Donkey Kong Country 2, Donkey Kong's father, Cranky Kong, created a challenge to see who could find the most secret DK coins on Crocodile Isle. Mario came in first, Yoshi came in second and Link came in last (Later on, Diddy Kong would claim the spot as number one). Earthworm Jim seems to have entered this competition as well, but didn't even come in third. This made him leave the island, and set down his ray-gun as evidence that he came.
Samurai Goroh
A character in the F-Zero series, Samurai Goroh is Captain Falcon's enemy and is a bounty hunter like him. Samurai Goroh is seen in the opening cinema of Super Smash Bros. Melee and the stage Mute City where he ends up crashing. He also appears as a trophy in the game.
Samurai Goroh's car the Fire Stingray appears in the opening cinema of Melee and also appears in Hinopio's Inn, in Super Mario RPG: Legend of the Seven Stars. However it is a toy version.
Samurai Goroh is a confirmed Assist Trophy for Super Smash Bros. Brawl.
Ridley
Ridley is a large, dragon-like alien and a character and the main villain in the Metroid series of games. In Super Smash Bros., Ridley can occasionally be seen flying in the background of the Planet Zebes arena.
Ridley also makes a brief appearance in the opening cinematic of Super Smash Bros. Melee, where he can be seen battling his archenemy, Samus Aran. A trophy of Ridley can also be obtained in Super Smash Bros. Melee. Recently, a compiliation of Ridley's theme music from various Metroid series games has been confirmed as being used in Super Smash Bros. Brawl.
Samus
In Super Mario RPG: Legend of the Seven Stars, if the player looks at Booster's doll, the player can spot a Samus doll.
Also, Mario can talk to Samus in the game. When Mario first reaches Land's End, avoid beating it. Go back to the Mushroom Kingdom and sleep in the guest room. When Mario wakes up, if Mario goes to Peach's room he'll see Samus sleeping, resting for her battle against Mother Brain.
In Wario Land II, There is a Crystal Metroid that is one of the treasures the player collects.
In Super Smash Bros., on the Planet Zebes stage, Wavers appear in the background most of the time.
Sonic the Hedgehog
Sonic the Hedgehog makes a cameo appearance in Donkey Kong Country 2. Like Earthworm Jim, Sonic competed in a contest to see who could find the most secret DK coins on Crocodile Isle. Like Earthworm Jim, Sonic didn't do very well, not evening placing third. Filled with shame, he left behind his trademark shoes. Sonic will also be in the upcoming game featuring both him and Mario at the olympics.
N&B Blocks
In the Mario Zone of Super Mario Land 2 features LEGO-like surfaces. They are not LEGOs, but N&B Blocks, a toy manufactured by Nintendo in the 70s.
Legend of Zelda
In Super Mario Bros. 3, the tune the warp whistle plays is also found in The Legend of Zelda. The whirlwind is from the same game.
In Super Mario RPG: Legend of the Seven Stars, Link appears sleeping at the Rose Town Inn every time Mario sleeps there. If Mario tries to talk to him, the Zelda discovery tune plays. In Stages 2-3 and 2-4 of Yoshi's Story, the name "Zelda" appears in the newspaper in the background.
In Wario Land II, the Ocarina of Time is one of the treasures the player collects. In Mario Golf for the Nintendo 64, the names of various Zelda characters appear on the score board. In the Gameboy version, the last club is called "Link's Club" and uses the Triforce as its logo. Also in Mario Golf: Toadstool Tour the player can see Triforce shaped coins.
Star Fox
When Mario visited Hinopio's Inn during the events of Super Mario RPG: Legend of the Seven Stars, he saw a model of an Arwing in the lobby. The Arwing is a recurring line of ships used by the Star Fox team.
In Mario Golf for the Nintendo 64, the names of various StarFox characters appear on the score board. Also the Arwing is a trophy in Super Smash Bros. Melee.
F-Zero
If the player goes to the lobby of Hinopio's Inn of Super Mario RPG, the player can see a model of Captain Falcon's Blue Falcon and Samurai Goroh's Fire Stingray.
Kirby
Kirby appears on a poster for the movie, Kirby's Story, in Mario & Luigi: Superstar Saga. Common Kirby enemies, Gordos, appear as enemies in Super Mario Land 2: Six Golden Coins, and Bronto Burts appear in the background of the Dream Land stage in Super Smash Bros. and Super Smash Bros. Melee.
King Dedede also appears in the background of the Green Greens stage.
Starfy
Starfy appears on a poster for the movie, "Legend of Stafy", in Mario & Luigi: Superstar Saga.
In Super Princess Peach, Starfy appears as the Starfish enemy.
(It should be noted that Wario made a cameo in the 3rd Stafy game for the Game Boy Advance)
Fire Emblem
One Toad in Paper Mario: The Thousand Year Door mentions that he enjoys Gameboy Advance games, especially Fire Emblem. Later on, Marth and Roy, both from Fire Emblem, fought in Super Smash Bros. Melee.
Currently, one Fire Emblem character, Ike, is confirmed to be a playable character in Super Smash Bros. Brawl.
Wolf O'Donnell
Wolf made a short cameo, in the beginning intro of Super Smash Bros. Melee, Wolf is seen in a space dogfight with his nemesis, Fox McCloud.
Wolf, along with many other villain characters, scored high in the character polls for Super Smash Bros. Brawl, but his appearance as a playable character is unknown.
Bruce Lee
Bruce Lee is a real world martial artist who was briefly mentioned by Mallow in the game Super Mario RPG: Legend of the Seven Stars. The character Lee, a martial artist Duplighost from the game Paper Mario, is possibly named after Bruce Lee.
