Here is the full list of all 19 Robbie Swifthand and the Orb of Mysteries achievements.
Discovered 25 secrets
Defeat the Second Guardian
Do a 720 degrees front flip!
Do a 360 degrees back flip!
Discovered 10 secrets
Defeat the First Guardian
Do a 360 degrees front flip!
Beat the tutorial in hell mode
Defeat the First Guardian without dying
Died 100 times
Discovered 40 secrets
Discovered 55 secrets
Discovered all secrets
Defeat the Third Guardian
Defeat the Evil One
Do what no mortal has done before
Do a 720 degrees back flip!
Do a 1080 degrees front flip!
Do a 1080 degrees back flip!