Sonic water

Probably one of the most well known effects on the console. Some zones in Sonic games have translucent water that covers the whole width of the screen:

Screenshot of Labyrinth zone 1 in Sonic 1, showing the water in the middle of the screen. The graphics look mostly orange above the water but they become green below it. The top of the water is covered with ripples made with sprites.

The effect is achieved using a raster effect that rewrites all palettes at the water height:

Screenshot showing all the palettes used across the screen. We can see all palettes changing at the point where the water is visible. We can also see a few garbage dots in that place, we'll get on that in the following paragraph.

You may notice there are a few garbage dots in the second screenshot: these are the so-called "CRAM dots", which show up wherever a color is written to the palette (and are visible because this is being done in the middle of the screen). The game covers this up using the ripple sprites, which are noisy enough that the CRAM dots get lost within them.