Here is the full list of all 40 Shantae and the Seven Sirens achievements.
Collect all Monster Cards.
Complete the game without any Health upgrades and all Heart Squids collected.
Avoid startling the Lobster Girl throughout the adventure.
Complete the adventure as quickly as possible!
Complete the adventure with 100% completion as quickly as possible!
Complete the game in Rule Breaker or Full Deck Mode.
Complete the adventure with 100% completion!
Unearthed all secrets.
Open all Shock Machines.
Shock a circus squid.
Witness every magical outcome with Slimes.
Turn an enemy to an ally by helping them heal.
Win the highest total in a Hula Contest.
Complete the adventure!
Complete the game in Beginner or Definitive Mode.
Defeated the Empress Siren.
Deactivate all the Towers.
Defeated the fifth Siren.
Obtain all magical forms.
Upgrade all magic to max.
Complete a Ghostly Quest.
Unearth a buried treasure.
Learn all magical dances.
Defeated the fourth Siren.
Revitalize cellular functions.
Locate the sunken ship remains.
Fell for a double cross.
Open a Shock Machine.
Ascend to Armor Town.
Defeated the third Siren.
Enter the Sea Lab.
Obtain the Lucky Amulet.
Defeated the second Siren.
Use the valve.
Have three Monster Cards equipped at once.
Uncovered a possible threat.
Reach Tree Town.
Defeated the first Siren.
Took the tour!
Obtain a Monster Card.