I myself have no idea about 8 and 11.
Level 12 is my own work, since the competiotion has ended:
You need to block the right side of the bottom green teleporter. So, that when you jump in the top teleporter, you come to the LEFT of the bottom teleporter. After that, jump up-right in the top teleporter.
You will come out at a trampoline, allowing you to jump up-right again to get to the exit.
To get to the coins near the trampoline, jump up-right from a different trampoline.
Hope that helps.
Oh, you have solved 2! In this case I back off everything I said, congratulate you, and ask YOU for advice!
