Algodoo

An even TRICKIER level, however, is Level 4 - 21, which is worth mentioning because it might just be one of the most difficult levels I've ever remade. You are given 6 Chucks to take down 6 pigs. Sounds simple enough until you realise the Corporal Pig is literally entrenched behind the larger platform. You could just bounce Chuck off the scene boundaries, but it takes LOADS of practice and patience to do that sucessfully.
If you're willing to give it a shot, click on my profile and download Level 4 - 21. Good Luck. You might need it...

I can't shoot the slingshot

@LAK_loves_ALGODOO

Here's how I would normally use the slingshot. This might help you.

Step 1: Place whatever bird you are trying to fling on the bottom hammock of the slingshot. Make sure it's secure. I usually use the drag tool to accomplish this but the move tool is also okay for this Step.
Step 2: Pull the bird backwards using the drag tool, not the slingshot ribbon. Don't pull it too quickly and don't pull it too far.
Step 3: Simply release the bird and watch those Piggy Towers crumble!

I do hope this helps you! And thanks for playing!