I did not think of that, thank you.
I tried it just now and it didn't work. I even added the bullet behavior to the fairy (which doesn't need the behavior because it's pinned to the propeller) and the fairy still goes through the platforms.
If the invisible propeller hits the platforms it does work correctly, just not the fairy.
(The funny thing is, I'd like to have that option if the player dies more than (maybe) 10 times on a level to make it easier for the player to win the level - just not every time)
C3 desperately needs a 'Concrete Solid' behavior and a 'Concrete Collision' option in events. So Many People make platform games using C3 and so often the game must be MacGyvered to work correctly because the solid behavior only works under certain circumstances, same with collisions.
I have a funny feeling I'm going to need that 'off set' option, which doesn't make much sense to me, but often works.
Off to google some more.