Here is the full list of all 60 Boomerang X achievements.
Kill 5 enemies with one boomerang recall
Target a Fly with the Oblivion Comet
Beat New Game +
Get 50 consecutive kills without touching the ground
Kill 10,000 enemies
Clear the Valley of the First Nymphs in under 2 minutes
Kill 2,500 enemies
Travel 200 miles in the air
Defeat the guardian at the heart of the scourge
Clear the Resonance Engine
Clear the Grave of the Yoran Legion
Clear Hall of the Ersatz Feast without using Flux
Clear the Hall of the Ersatz Feast
Kill 1,000 enemies
Clear Atsil’s Quarry
Clear the Old Vein
Clear the Incursion of the Great Worm
Clear Incursion of the Great Worm without using Flux
Clear the Poisoned Well
Clear the Poisoned Well without using Flux
Clear Yoranwood
Clear the Yoranwood without using Flux
Clear the Valley of the First Nymphs
Clear the Valley of the First Nymphs without using Flux
Clear the Grudge Pit
Clear the Grudge Pit in under 2 minutes
Clear the Grudge Pit without using Flux
Kill 100 enemies
Clear Kenak, the Exiled Tyrant in under 2 minutes
Clear Kenak, The Exiled Tyrant
Clear the Composer’s Garden
Get the boomerang
Listen to all of Tepan’s Tales
Chain 5 Needle shots in a row
Kill 10 enemies while the boomerang orbits you
Beat a level without touching the ground
Jam out on the strings in the Tuning Court
Beat the game in under one hour
Beat the game in under 45 minutes
Beat the game without taking damage
Clear the Yoranwood in under 2 minutes
Clear the Poisoned Well in under 2 minutes
Clear Incursion of the Great Worm in under 3 minutes
Clear the Old Vein in under 3 minutes
Clear Atsil’s Quarry in under 3 minutes
Clear Hall of the Ersatz Feast in under 3 minutes
Clear the Grave of the Yoran Legion in under 3 minutes
Clear the Resonance Engine in under 7 minutes
Clear Vashkatar in under 3 minutes
Clear the Old Vein without using Flux
Clear Atsil’s Quarry without using Flux
Clear the Grave of the Yoran Legion without using Flux
Clear the Resonance Engine without using Flux
Clear Vashkatar without using Flux
Beat a level in "Scattershot Only" mode
Play every non-custom endless category.
Get at least 1500 points in the Hardcore category.
Get to a x10 multiplier in endless mode in any category.
Kill a giant moth in the Passionfruit category.
Survive for 2 minutes while the floor is covered in lava in endless mode in any category.