Bloodstained: Ritual of the Night features several playable characters, but it's also possible to take on the guise of another famous character, as the player can alter Miriam's appearance so that she looks like Shovel Knight and can use his mighty tool in battle.
It had previously been revealed on the Bloodstained: Ritual of the Night Kickstarter page that a collaboration was planned with Yacht Club Games that would involve adding Shovel Knight into the game in some capacity. Bloodstained: Ritual of the Night is now out and the details of the collaboration have been revealed.
It's possible to encounter an enemy in Bloodstained: Ritual of the Night called the Shovel Armor, which looks like Shovel Knight. If you keep farming these enemies, then you will gain a Shovel as a weapon and can earn a Shard that allows you to summon a Shovel Armor into battle. The Shovel Armors can be found in the Forbidden Underground Waterway.
There is a 3% chance that killing a Shovel Armor will result in it dropping an EX Shovel Armor item. In Bloodstained: Ritual of the Night, there are some items that change Miriam's appearance, but these are mostly hats. If the player equips the EX Shovel Armor, then Miriam's appearance will switch to that of a Shovel Armor, which is meant to resemble Shovel Knight.
Equipping the EX Shovel Armor will switch the player's weapon to the Shovel and will give them access to a digging attack that thrusts dirt at the enemy. The description of the EX Shovel Armor claims that it was formerly worn by a certain valiant knight, which clearly refers to Shovel Knight.
Shovel Knight was also funded by Kickstarter, so it makes sense that too similar projects would reference each other. The fans might still be waiting for Shovel Knight: King of Cards, but they can at least explore the dangerous castle from Bloodstained: Ritual of the Night in the guise of their favorite hero.