Thanks a lot ! It was easy but very long to set up.
You need, a big background
See pictures below : every part of the background is divided in triggers.
At the beginning you insert your 9 blocks actors in the scene (limit is 10 but 1 is the reward, so you can use only 9 for the blocks).
Each time the player is in a specific place, he will activate a trigger and will thus move blocks (not all, only half the blocks, for example actors 5-6-7-8 in the top-center in pink ). In some place, a block is a simple image drawn in the background with a collision on it.
I hope that can help you (and others) to make great games !