This page explains in detail the interactions between the Kirby series and the Mario series.
Kirby's Dream Land
April 27, 1992
Kirby
Mario
Some of the enemies in the game resemble Mario enemies, most notable the Ghost Booler, that looks very much like Boo, and Two Face, a hovering mask that looks and behaves like Phanto from Super Mario Bros. 2 (USA).
Other similarities, that however may just be coincidences, are in Blipper, a fish with googles that resembles Blurp from Super Mario World, and Squishy, a squid-like enemy resembling a Blooper.
Some people also feel the Waddle Dee, the most common enemy in the game, to have some connection to the Goomba, the most common enemy in the Mario series, but this may only be due to their role.
Finally the enemy Chuckie, comes out of a box with a "?" on it, thus resembling Mario's "? Block", but this may be a coincidence. This also applies to Hurly, its replacement in Extra Mode. It must be noted that the box looks nothing like a "? Block" in artworks, except for the question mark.
All these enemies, except for Two Face, also appear in later Kirby episodes, keeping their appearances.
Super Mario Land 2: 6 Golden Coins
October 21, 1992
Kirby
Mario
TheUnibo enemy in the game is very similar to the Gordo from Kirby, and may actually be based on it.
It's possible, though, that it was only created as a smaller version of the Unira from Super Mario World and its resamblance to the Gordo to be a coincidence.
Club Nintendo Comics
Kirby
Mario
Kirby is featured in various Mario comics published on Club Nintendo.
Super Mario-kun
Kirby
Mario
Kirby makes an appearance in an episode of Super Mario-kun, where he shows up inhaling two enemies and scaring Mario in the process.
Mario Kirby Meisaku Video
1996
Mario
Kirby
The Mario Kirby Masterpiece is an animated movie featuring two different stories, a Mario one and a Kirby one, but they do not interact in any way, so this is not considered a crossover, but rather a two movie bundle.
Kirby Super Star
March 21, 1996
The game features many Mario references, and they are all still featured in the remake Kirby Super Star Ultra, that also features some new ones.
A notable reference, present in all minigames is in Kirby' Stone ability, that has him very rarely turn him into a golden statue of Mario. Other golden statue forms are a Samus Statue, based on Samus Aran from Metroid and the HAL logo.
Spring Breeze
Kirby
Mario
This mode is basically a remake of Kirby's Dream Land, with graphics redesigned. The final battle with King Dedede now features an audience cheering in the background, mostly composite of enemies from the game, but in the extreme left and right sides of the scenario, Mario characters can clearly be seen. These are Mario, Luigi, Toad, Birdo, and, barley visible, Peach. There also is Bowser behind them, but he's almost not visible at all (his appearance is confirmed checking the sprites in the game's code).
Their appearance on the right side is mirrored from the one on the left, but the left one is the original one, as can be seen by Luigi's "L" on the hat.
Megaton Punch
Kirby
Mario
This minigame features the same crowd from "Spring Breeze", but Peach and Bowser can't be seen, except for Peach's hair, just barely.
Unlike Spring Breeze, this minigame was left graphically unchanged in Kirby Super Star Ultra.
The Great Cave Offensive
The Great Cave Offensive's Treasure screen. Mario items are the Zebra Mask (row 1, col. 9), the Bucket (row 3, col. 3) and the Turtle Shell (row 4, col. 1).
Kirby
Mario
This mini-game features 60 collectable treasures, many of which are actually items from other Nintendo games. Mario items are:
The Zebra Mask. While its name is different, it is actually based on the Phanto enemies from Super Mario Bros. 2 (USA), as confirmed in Kirby Super Star Ultra.- The Bucket, having a "M" on it, is most likely based on the bucket from Mario & Wario, however it's white instead of blue/purple.
- The Turtle Shell is likely based on Koopa Shells from the Mario series, even if they look different. This is confirmed in Kirby Super Star Ultra.
Other treasures include the Screw Attack from Metroid, Falcon Helmet from F-Zero, Mr. Saturn from Mother, Kong's Barrel from Donkey Kong, the Pegasus Wing from Kid Icarus and the Triforce from Zelda.
Paper Mario
Bowser holding the Star Rod.
August 11, 2000
Kirby
Mario
An item called Star Rod appears in Paper Mario; it has the ability to make wishes come true and is used by the Star Spirits in Star Haven to grant people's wishes. During the events of the game it's stolen by Bowser, who uses it to make his own evil wishes come true.
This rod is named like the Star Rod from Kirby's Adventure and its look seem to be based on it (aside from the star on top, the white and red stiped handle is unlikely a coincidence). In its original appearance it's used as a weapon by Kirby, being able to shoot stars. However its power is known to go beyhond this, being able to give good dreams to the people of Dream Land while placed on a Fountain of Dreams. During the game's events it is split in seven pieces by King Dedede to hide it from Nightmare, finally being found and restored by Kirby.
It is arguable if the Star Rod in Paper Mario should be considered the same rod, because their history is different, but since the two games are supposed to happen in two different continuities anyway, it's possible to consider them two different versions of the same item, from two different universes.
Another Star Rod appears in Mario Party 8.
Mario & Luigi: Superstar Saga
The "Kirby Story" poster, along with a Wario poster, a Mario & Luigi poster and a Legend of Starfy poster.
November 17, 2003
Kirby
Mario
In the Yoshi Theatre zone, four movie posters can be seen, one of which is a movie about Kirby titled "Kirby Story", and the image shows the hero riding a Warp Star. The movie's name may be a pun on Mario Story, the japanese title for Paper Mario, since that game featured a Kirby reference.
Mario Party 8
The Star Rod in Mario Party 8.
Kirby
Mario
A Star Rod is featured in the game, where it's the reward for becoming "Superstar" at the Star Carnival, but is stolen by Bowser. Its name is the same as the item from Kirby's Adventure, but its design is very different, despite still having a striped handle and star on top. Even if this is not a coincidence, the rod may be actually based on the Star Rod from Paper Mario, making only an undirect reference to the Kirby series.
Kirby Super Star Ultra
September 22, 2008
All the references from Kirby Super Star return, but there also are new ones in some of the mini-games:
Spring Breeze
Kirby
Mario
Since this mini-game's graphics has been redesigned, the Mario character's cameos in the background has changed too: Mario, Peach and some Toads are now in the audience to the left of the ring, while Luigi, Wario and other Toads can be seen on the right of it.
The Great Cave Offensive
The Great Cave Offensive's Treasure screen from Kirby Super Star Ultra. Mario items are the Phanto Mask (row 1, col. 9), the Bucket (row 3, col. 3) and the Koopa Shell (row 4, col. 1).
Kirby
Mario
The three Mario items from the previous game return, but the Zebra mask is now renamed Phanto Mask to directly reference the Phanto enemy from Super Mario Bros. 2, and the Turtle Shell is renamed Koopa Shell and is redesigned to look more like recent designs of the shells in the Mario series, specifically resembling those from the Mario Kart sub-series.
Revenge of the King
Kirby
Mario
Fight with Kabula.
Kabula, an aircraft that served as a boss in Kirby's Dream Land, returns here with a redesigned appearance, now having a smiling face painted on "her". Sporting long eyelashes, this was done possibly to give "her" a femine appearance, justifying why she's officially considered female.
Her face looks very similar to the face of Mario's Bullet Bill in some games, such as Super Mario Land 2. The face is also present on some missiles she shoots, thus looking almost exactly like Bullet Bills.
Also a golden statue of Mario appears at the end of the mini-game's credits.
NES Remix 2
April 24, 2014
Kirby
Mario
Stage 4 of the Remix I challenges is based on Kirby's Adventure, featuring its HUD from the game, and the player controlling Kirby, however the enviroment itself is made of blocks from the Mario series, specifically from Super Mario Bros.: The Lost Levels, and there are 10 coins actually based on the ones from Super Mario Bros. 3, and the objective is to collect them all in 60 seconds. The graphics are based on underground sections of The Lost Levels, with blue bricks and black background, but the level design is not based on any actual area from the game. The gameplay is just like in Kirby's Adventure, with the Brick Blocks acting like Star Blocks, being destroyed by Kirby's attacks or inhaled, and they can't be destroyed or bounced by hitting them from below, unlike Brick Blocks in the Mario series, therefore the difference is only graphical. Also Coins don't award any point. The background music is the Kirby's Adventure track "Forest Trail".
Stage 6 of the Remix I challenges is set at the fight against Whispy Woods in Kirby's Adventure, but there also are four large Boos from the Mario series attacking Kirby from behind. These are specifically based on Super Mario Bros. 3, which is featured in NES Remix 2, but they're very large, possibly being based on the Big Boo enemy from later games in the Mario series. Like in the original game, Boos will only attack Kirby when he's not facing them, and they will cover their faces otherwise.
Stage 11 of the Remix I challenges is based on Super Mario Bros. 2, with the player controlling Toad, but the stage is actually set in the world from Kirby's Adventure, specifically the first area of the first level, Vegetable Valley, featuring Star Blocks, two Waddle Dees and a Poppy Bros. Jr. The enemies reflect the way they acted in the original game, with Waddle Dees walking back and forth and Poppy Bros. Jr. hopping around, but they're actually just reskins of Shy Guys and Tweeter, and this can be noted by the fact that Waddle Dees don't walk down platforms and Poppy Bros. Jr. hops in the Tweeter's specific pattern and is not animated; also Star Blocks can be picked up and thrown without breaking, acting the same way as Mushroom Blocks in Super Mario Bros. 2. The background music is the Kirby's Adventure track "Green Fields".
Stage 10-4 of the Bonus challenges is set at the fight against Nightmare's Power Orb in Kirby's Adventure, but there also are large Bullet Bills from the Mario series flying by, hurting Kirby. These are based specifically on their appearance in Super Mario Bros.: The Lost Levels, which is featured in NES Remix 2.
License
Copyrights for both series are held by Nintendo.