Here's what you need to do to unlock every character in Shovel Knight Showdown, for each character you want to unlock you'll need to beat story with a different character (save one), difficulty doesn't matter so feel free to unlock all of them on easy if you want. To keep this simple, I will list all the characters that are unlocked in sequence after the first one used to unlock a character in that sequence, I know that doesn't make too much sense but if you look down at the guide you'll know what I mean.

• Mona
  
• Liquid Samurai (Beat story with mona)

• Tinker Knight
  
• Mole Knight (Beat story with Tinker Knight)
  
• Treasure Knight (Beat story with Mole Knight)

• Phantom Striker
  
• Dark Reize (Beat story with Phantom Striker)
  
• Reize (Beat story with Dark Reize)

• The Enchantress

And now we come to the last set of special unlocks, remember that odd one out I mentioned before, well here he is.

• Baz (Beat story mode without losing a fight (AKA don't lose a life/continue)

Meanwhile after unlocking him, he can be used to unlock the final two characters

[Baz Unlocks]

• Mr. Hat
  
• Goldarmor (Beat story with Mr. Hat)

Well there you have it, everything you need to do in order to unlock all the characters! Hope this helps, good luck on your future battles!