to fly, go to the "hill" with many marble pillars. go to the main one on top of the hill. go to the "dais". wait there for a while. read the instructions.
i found 22 hardest, due to my poor reaction skills at the time, but, retrying, i managed to do it first time, and level 25 after 4 tries. definite 5/5.
 "Music Catch 2")
 "Super Stacker 2")
 "Aubergine Sky")
 "Kowlr")
 "Open Doors 2")
 "William and Sly")
 "The Space Game: Missions")
 "Phage Wars 2")
 "Kingdom of The Wind")
 "Crunchball 3000")
 "Run")
 "Spewer")
 "Synapsis")
 "The Great Sperm Race")
 "Super Karoshi")
 "Red Remover")
 "Hedgehog Launch")
 "me and the key")
 "Meat Boy")