Here is the full list of all 123 Cassette Beasts achievements.
Open a door long since thought lost.
Defy all odds in a place between worlds.
Observe 120 different species
Solve the riddle of Morgante's song.
Reopen every station
Defeat Babelith
Get the Fusion Radar
Defeat Ianthe and become a Ranger Captain
Defeat Captain Codey
Visit every part of New Wirral
Help Sunny start a new life
Complete Barkley's quest
Obtain the Averevoir Flight ability
Obtain an Ice-type bootleg
Unlock Barkley
Enter a romantic relationship
Defeat Captain Heather
Defeat Captain Gladiola
Defeat Lamento Mori
Complete Morgante's song
Complete Viola's quest
Obtain an Earth-type bootleg
Bring Viola to the shipwreck
Unlock Viola
Defeat 20 Rogue Fusions
Complete Eugene's quest
Obtain the Pumpkin Vine Ball ability
Complete Felix's quest
Meet Kuneko at 4 altars
Meet Kuneko at 3 altars
Meet Kuneko at 2 altars
Meet Kuneko at 1 altar
Meet Kuneko
Get to 5 hearts with Kayleigh
Defeat Alice
Defeat Captain Buffy
Clear 5 Landkeeper offices
Defeat Captain Cybil
Obtain 50 different species
Find a helping hand in a place far away.
Find yourself somewhere far away.
Defeat Captain Lodestein
Defeat Heckahedron
Unlock Felix
Defeat 10 Rogue Fusions
Clear 4 Landkeeper offices
Defeat Captain Clee-O
Complete Meredith's quest
Defeat a ghost
Bring Meredith to the mall
Help Hoylake with his research
Defeat a Swarm
Defeat 5 Rogue Fusions
Defeat Captain Wallace
Meet the Travelling Merchant
Complete Kayleigh's quest
Defeat Captain Zedd
Clear 3 Landkeeper offices
Obtain a rare sticker
Defeat Captain Penny Dreadful
Obtain the Bulletino Dash ability
Defeat Captain Judas
Defeat Captain Skip
Obtain a Water-type bootleg
Clear 2 Landkeeper offices
Obtain the Diveal Swim ability
Obtain the Electromagnetism ability
Obtain 20 different species
Defeat Poppetox
Unlock Meredith
Meet the one who dutily attends the stations.
Investigate a rumour
Start Kayleigh's quest
Choose a design for Harbourtown's sign
Defeat a Rogue Fusion
Obtain 10 different species
Sign up to the Rangers
Remaster a tape
Obtain a rumour
Clear 1 Landkeeper office
Unlock Eugene
Complete the tutorial
Obtain the Mothwing Glide ability
Unlock Kayleigh
Obtain Bansheep
Obtain Candevil
Defeat an Unstable Fusion
Defeat an Orb Fusion
Defeat 50 Rogue Fusions
Obtain 100 different species
Obtain 120 different species
Obtain additional data on every species
Obtain a Beast-type bootleg
Obtain a Fire-type bootleg
Obtain a Plastic-type bootleg
Obtain a Plant-type bootleg
Obtain a Poison-type bootleg
Obtain an Astral-type bootleg
Obtain a Lightning-type bootleg
Obtain an Air-type bootleg
Obtain a Metal-type bootleg
Obtain a Glass-type bootleg
Obtain a Glitter-type bootleg
Obtain a monster form thought impossible to find.
Get to 5 hearts with Eugene
Get to 5 hearts with Meredith
Get to 5 hearts with Felix
Get to 5 hearts with Barkley
Get to 5 hearts with Viola
Defeat an ancient force brought back to full strength.
Overcome the essence of fusion.
Come face-to-face with a faceless being.
Complete Frankie's training
Complete Vin's training
Complete 5 noticeboard quests
Complete 20 noticeboard quests
Complete 50 noticeboard quests
Complete 100 noticeboard quests
Try to sneak past a battler by jumping over their head
Win a battle before it starts
Win a battle while ghostly
Win a battle while Gambit is active
Prove your worth to a certain warrior.