Here is the full list of all 11 Reed 2 achievements worth 1,000 gamerscore. It takes around 1-2 hours to unlock all of the achievements on Xbox One.
Find the hidden Horse.
Find about the Sword you can't pick up....
Find the 3rd hidden level.
Find the hidden Arcade Machine.
Find snow on a level.
Find the hidden Duck.
Find the 2nd hidden level.
Find the hidden character from Prisonela.
Find the 1st hidden level.
Die once.
Get your first cube.