Shovel Knight has appeared in several other games and media as a testament to his popularity. So far only Shovel Knight and Plague Knight are the only ones from the Shovel Knight universe to have appeared in other works.
It should be noted that Reize Seatlan, Baz, Kratos and the Battletoads are all characters who originate from outside of Shovel Knight and are thus cameos in Shovel Knight.
Playable appearances
Runbow
Shovel Knight in Runbow
Shovel Knight makes a playable appearance in the Wii U game Runbow. He is unlocked by performing a butt pound ten times. His method of being unlocked is likely a reference to the Shovel Drop being an attack that hits enemies from above. Alternatively it could be a reference to Shovel Knight's Butt Mode.
Shovel Knight & Brick M. Stonewood in Starr Mazer
Starr Mazer
On February 10, 2015 Imagos Softworks announced that Shovel Knight would be a playable crossover character in their upcoming game Starr Mazer.
Cook, Serve, Delicious: Battle Kitchen
Shovel Knight, among other indie characters, appears as a playable character in the game Cook, Serve, Delicious: Battle Kitchen.
Road Redemption
Shovel Knight is now one of the selectable characters in Road Redemption.
Move or Die
Promotional image for Shovel Knight's Move or Die character
Shovel Knight appears as a playable character in the four player multiplayer steam early access party game.
Dino-Run DX
Shovel Knight is set to appear as a Dinosaur in this Indie runner game.
Ghost Police
On July 9, 2016, Steven McCarthy announced that Shovel Knight would be appearing in his indie game, Ghost Police. Shovel Knight will be an NPC/boss in the main story, but will also be playable in his own separate campaign that features a completely different gameplay style. Steven mentioned that he would be working with Yacht Club Games to keep the gameplay "faithful and fresh at the same time" and noted that those who have played the Bangai-O series would note the similar gameplay style, albeit with some differences in execution.
Indivisible
Shovel Knight has been announced to join the cast of the RPG game Indivisible as a guest character.
Blaster Master Zero
Shovel Knight, along with Shantae from the Shantae series, appears as a playable character in Blaster Master Zero.[1]
Runner 3
Shovel Knight in Runner 3.
Shovel Knight will be a playable character in the upcoming game, Runner 3.
Blade Strangers
Shovel Knight appears as a playable character in the crossover fighting game Blade Strangers.[2]
Guest and Cameo appearances
Bloodstained: Ritual of the Night
Shovel Armor in Bloodstained.
Concept art of a more realistically proportioned Shovel Knight was drawn up by one of the character designers working on the indie title Bloodstained, called Shovel Armor. The artist in question, Yuji Natsume, claims to be a fan of the character, and that it is simply fan art.
However on June 11, 2015, it was confirmed that Shovel Armor will be appearing in Bloodstained. What his role in the game will be is currently unknown.
The Reward: Tales of Alethrion
Shovel Knight, (or a person in Shovel Knight's signature Stalwart armor) has a brief cameo appearance in Sun Creature Studio's animated series Tales of Alethrion (in the episode First Hero, around 10:55 mark), likely due to the mutual support between Yacht Club Games and Sun Creature Studios in their respective Kickstarter projects.
Crypt of the NecroDancer
The Pawnbroker, one of the shopkeepers in Crypt of the Necrodancer, has items from various indie games among his wares, including Shovel Knight's Stalwart helmet.
Creepy Castle
Plague Knight and Shovel Knight with Monsoon, one of the characters from Creepy Castle
Shovel Knight and Plague Knight, as well as other indie characters, makes an appearance in the game Creepy Castle.
Pixel Noir
Shovel Knight has been announced to appear in Pixel Noir in some fashion.
Azure Striker Gunvolt 2
Shovel Knight's Gunvolt 2 Cameo Teaser!
Shovel Knight appears in Azure Striker Gunvolt 2 as a secret boss character. He can be fought by scanning the Shovel Knight amiibo into the game.
Yooka-Laylee
Shovel Knight makes a cameo in Yooka-Laylee as an NPC.