Each world has four levels, the grid gets larger but it's not too consistent.

World 1 - "Remove tiles with a circuit"
Pretty basic. There are colored tiles here.

World 2 - "Tiles have weight this time around."
Monochrome tiles that have gravity, so removing one block causes the column to fall closer to the ground. Not too hard especially as many of them are next to each other.

World 3 - "Tiles may switch places at anytime."
Rainbow gradient tiles, though it doesn't look like they'll switch while you've got one selected. Often times the switched tiles actually make it easier, so if there's tiles that just won't go, there's a chance the game will fix that for you.

World 4 - "Some tiles are stubborn."
The metal tiles here among the colored ones don't have matches and aren't selectable. Basically they make it harder to make a circuit, you'll have to clear out others first. They'll still remain after you clear out the map.

World 5 - "Stubborn and heavy."
Monochrome tiles again from World 2 with the stubborn tile gimmick. This makes it easy to get stuck, so hope you saved up on those screwdrivers.

World 6 - "Can't seem to stay down."
Rainbow gradients are back, with new tiles sometimes appearing. The good news is that they seem to be pretty easy to match when they do appear, and they don't switch places anymore.

World 7 - "Stubborn and indecisive."
This one brings back the colored tiles but combines the stubborn tile gimmick from World 4 and the switching tiles from World 3.

World 8 - "Very tough."
The monochrome tiles have all four gimmicks—weight, switching, stubborn, and new tiles. There are five levels in this world, but once you complete it, you beat the game!