Here is the full list of all 20 Shovel Knight: King of Cards achievements.
Finish New Game Plus.
Finish a Joustus Judge stage without dying or collecting any food or health hearts.
Use only heirlooms to defeat any boss!
Collect all Merit Medals.
Obtain all Joustus cards.
Find and complete all stages and stage paths, and defeat all wandering travelers.
Defeat every possible Joustus opponent.
Acquire all armor, heirlooms, fancy things, and upgrades.
Commission a finished portrait!
Lose a unique card, then win it back!
Clear all 4 houses of Joustus, and win the final battle...
Use each one of Chester's Cheat Cards.
Clear all 4 houses of Joustus without buying or reclaiming cards from Chester. (Not in New Game+)
Find King Knight's secret room!
In a Joustus match with more than one gem, win by claiming every gem.
Finish the game.
Complete the game in fewer than 25 stages.
Finish the game without acquiring any heirlooms, health upgrades, or vigor upgrades. Armors are ok!
Beat the game within 1 hour and 30 minutes.
Finish a stage and jump fewer than 10 times.