Here is the full list of all 25 Poi achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Find all of the hidden costumes.
Find a hidden hat.
Collect ALL the Explorer Medallions.
Kick a Bucket Head.
Find the legendary treasure.
Take a picture of ALL the creatures.
Meet the requirements to open the Mysterious Gate.
Take a picture of the Master Explorer.
Visit the hidden planet.
Discover ALL the Locations.
Find ALL the Golden Gears.
Rescue all the baby Pin Birds.
Collect all the Explorer Medallions in Crystal Cavern.
Collect all the Explorer Medallions in Sinking Sands.
Collect all the Explorer Medallions in Mount Magma.
Hey, watch where you're rolling!
Collect all the Explorer Medallions in Cozy Canyon.
Collect 10 Explorer Medallions.
Do a triple jump.
Find ALL the Fossils.
Sometimes, things don't always go as planned.
Discover the mysterious travelling merchant.
Purchase an item from the shop.
Earn your first Explorer Medallion.
Beat the game in New Game+ mode.