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I managed to get all three on Back and Forth like this: 1) click under the green guy to put him on the platform, 2) move the platform to the cat, 3) drop the cat, 4) move the platform back, 5) drop the army guy, 6) shoot the laser at the crates, 7) and again for the next ones, 8) remove the top of the two sloped bits, 9) click under the blue guy so he and the crates drop and then 10) time the laser so it hits the crates as they fall. I managed to get three of them, and the blue guy fell over the other one to the cat below. Hope it helps!
Under rating threshold (hideshow)
I modified strayjohno's Back and Forth technique a little. Remove step 4 (leave the platform at the far side). Then move the platform back at the end and the blue guy will squirt up into it.
Under rating threshold (hideshow)
Made "tricky portals"
How to do it:
1: Make the crate fall.
2: Click the other portal.
3: Shoot 1 time and make the LOWER crate explode.
4: Click the switch.
5: Click the other portal when the cat hit the portal.
it worked for me in 1 time, but it can be that the cat doesn't fit always through just the lower block, just keep trying!