1. Mix Blops to get the right color.
2. Passing over a black square = death.
3. Cubies with arrows on them indicate that they can rise and fall. In the up position, they act as walls.
There are 120 Free Levels and I solved about 85 of them pretty quickly, including the last 40, theoretically the hardest. They're not hard.
The 60 Premium levels are in Platforms 7, 8 & 9. I got to do 1 in each for free. These included new elements like reflectors and squares that redirected your Blop's paths.
I really like the graphics overall. There's a good deal of charm here. Casual puzzlers will enjoy Smoosh!