Here is the full list of all 31 Sir Fallen achievements.
Jump 1000 times
Use the upper training slope to start your run.
Beat the game once on any mode
Beat the Sir Fallen demo
Make it to the top without hitting a spike.
Activate all flags at least once in a single run.
Visit Wolf Tower
Finish a run in 1 hour or less.
Jump 25,000 times
Jump 100,000 times
Land on spikes 100 times
Land on spikes 500 times
Land on spikes 5000 times
Land on a slope 100 times
Land on a slope 500 times
Land on a slope 5000 times
Walk a mile
Walk a half marathon
52,427 steps taken
Finish a run in 30 minutes or less.
Finish a run in 15 minutes or less.
Reach Hell Castle.
Fly into space.
Find the bananas
Bounce over the top of Arcane Tower
Find the observatory room.
Set up the picnic.
Find your mislaid towel.
Find your basket.
Find the white rose.
Find the sword in the stone