Spoiler: To start tap lowest red block till B comes up, tap slider back inside and quickly slide up , wait till he falls. If more hints are needed leave a comment. I made a few alternate paths for those who miss the main path but you'll have to use TOA to get back on.
There is so much happening inside its hard to know what the gameplay is. My first attempt seemed to be a cul de sac but then it moved and B was stuck. Took the other option next attempt and surprisingly short path to win. Seemed too short to be designed gameplay .
The level of guesswork is high and I haven't even seen the win. After finding a fairly quick path to the top, I was surprised my screen went black. But as always fun to explore.