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.
Defeat 20 Rogue Fusions
Solve the riddle of Morgante's song.
Defeat Babelith
Complete Morgante's song
Defeat Lamento Mori
Visit every part of New Wirral
Defeat Ianthe and become a Ranger Captain
Defeat Captain Clee-O
Defeat Captain Cybil
Defeat Captain Judas
Defeat Captain Zedd
Defeat Captain Codey
Complete Viola's quest
Bring Viola to the shipwreck
Unlock Viola
Help Sunny start a new life
Defeat Captain Heather
Defeat Captain Gladiola
Complete Eugene's quest
Clear 5 Landkeeper offices
Clear 4 Landkeeper offices
Defeat Captain Skip
Get to 5 hearts with Kayleigh
Defeat Captain Buffy
Meet the Travelling Merchant
Complete Barkley's quest
Obtain an Ice-type bootleg
Unlock Barkley
Obtain a Beast-type bootleg
Obtain the Pumpkin Vine Ball ability
Find a helping hand in a place far away.
Find yourself somewhere far away.
Defeat Alice
Obtain an Earth-type bootleg
Complete Felix's quest
Meet Kuneko at 4 altars
Meet Kuneko at 3 altars
Meet Kuneko at 2 altars
Defeat Captain Lodestein
Defeat 10 Rogue Fusions
Meet Kuneko at 1 altar
Clear 3 Landkeeper offices
Clear 2 Landkeeper offices
Defeat Captain Penny Dreadful
Complete Meredith's quest
Defeat a ghost
Bring Meredith to the mall
Unlock Meredith
Defeat Captain Wallace
Meet Kuneko
Unlock Felix
Defeat a Swarm
Defeat 5 Rogue Fusions
Defeat Poppetox
Obtain 20 different species
Obtain the Electromagnetism ability
Obtain the Diveal Swim ability
Investigate a rumour
Complete Kayleigh's quest
Choose a design for Harbourtown's sign
Obtain the Bulletino Dash ability
Obtain 10 different species
Defeat a Rogue Fusion
Start Kayleigh's quest
Remaster a tape
Meet the one who dutily attends the stations.
Sign up to the Rangers
Obtain a rumour
Clear 1 Landkeeper office
Unlock Eugene
Complete the tutorial
Obtain the Mothwing Glide ability
Obtain a rare sticker
Unlock Kayleigh
Obtain Candevil
Obtain Bansheep
Defeat an Unstable Fusion
Defeat an Orb Fusion
Defeat 50 Rogue Fusions
Observe 120 different species
Obtain 50 different species
Obtain 100 different species
Obtain 120 different species
Obtain additional data on every species
Obtain a Fire-type bootleg
Obtain a Plastic-type bootleg
Obtain a Plant-type bootleg
Obtain a Water-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 the Averevoir Flight ability
Get the Fusion Radar
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
Enter a romantic relationship
Reopen every station
Defeat an ancient force brought back to full strength.
Defeat Heckahedron
Overcome the essence of fusion.
Come face-to-face with a faceless being.
Help Hoylake with his research
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.