Here is the full list of all 19 Cold Iron achievements.
Defeat Whiskey Sweet with an A rank or better.
Defeat Riverboat Diaz with an A rank or better.
Unlock all other achievements.
Complete the game from start to finish without dying.
Win a round in under 0.2 seconds.
Destroy every watermelon in three bonus levels.
Find a creative way to overcome Riverboat Diaz.
Defeat Black Jack with an A rank or better.
Defeat Will O' Wisp with an A rank or better.
Defeat The Tempest with an A rank or better.
Defeat Nowhere Man with an A rank or better.
Defeat Iris with an A rank or better.
Defeat A.U. 117 with an A rank or better.
Defeat The Behemoth with an A rank or better.
Defeat The Gunsmith with an A rank or better.
Defeat Cold Iron with an A rank or better.
Discover the secret chicken in three worlds.
Collect every silver (or golden) statue.
Collect every golden statue.