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