ladders would be easy
Use an actor variable integer "canClimb"
When you collide with a ladder canClimb = TRUE;
When you end collision with a ladder canClimb = FALSE;
If you are next to a ladder and canClimb == TRUE then pressing up makes you go up.
Bugga. I just noticed that M has already said this!
Moving platforms? Moving them is easy. Jumping on and off of them is tricky! When you solve that one tell me!