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