Birds'n'Blocks 2 has you drop birds onto a small platform. You have to get your birds on their platforms by removing blocks from under the birds so that they fall in certain directions. The in-app purchase is called a “Level skip,” where you may skip the level you stuck on by paying. The problem is that some levels are unbeatable, which forces players to pay to continue playing. In-game physics are unrealistic due to poorly optimized momentum mechanics.