Here is the full list of all 28 Unravel Two achievements.
Complete Nightswimming
Complete Little frogs
Complete a level in co-op
Customise a character
Complete Hideaway
Complete Foreign shore
Complete Is that all there is
Complete Ashes to ashes
Complete At the rapids
Complete Hideaway in one go without dying
Complete Little frogs in one go without dying
Complete Nightswimming in one go without dying
Complete Is that all there is in one go without dying
Complete Ashes to ashes in one go without dying
Complete At the rapids in one go without dying
Earn the gold medal in Hideaway
Earn the gold medal in Little frogs
Earn the gold medal in Nightswimming
Earn the gold medal in Is that all there is
Earn the gold medal in Ashes to ashes
Earn the gold medal in At the rapids
Earn a medal for achieving a time or not dying on any level
Complete any bonus level
Complete all of the bonus levels in under 45 minutes in one go
Travel from the island with the tables back up to the lifebuoy in At the rapids
Travel between the two barrels in At the rapids without touching the water
Make it between the two moose signs in Ashes to ashes without using any directional inputs
Survive 5 pike attacks in a row without using your lasso in the pike chase