Here are some screenshots of interesting pictures from the Sega Genesis, taken with my low-quality video capture card.
This is the source image for several of these pics, from the game Castlevania: Bloodlines. The particular level I'm on uses mid-frame raster effects, so I can modify sections of the screen while being able to see the rest for a reference.
Here's the same image, with the resolution switched to 32-cell mode then back to 40-cell mode halfway through the display. If you ignore the offset position, you can see the display is much wider.
This picture has the display switched into mode 4 (SMS compatible) in the middle. Notice that for the extra 8 columns at the right edge of the display, 'garbage' data is fetched for the name table attributes. This is because mode 4 is normally 32 columns wide.
More mode switching, this time it's what appears to be TMS9918 mode 0. No patterns appear inside the colored text blocks, however. The palette is taken from CRAM, and is not fixed like the TMS9918.
Now I'll show you the infamous window bug. Here's the source image, and note that for the middle section of the display, the lower four bits of the horizontal scroll value are equal to zero. (The bit of garbage on the left side is the window plane; there's no easy way to define some sensible name table data for it.)
In this pic, the lower four bits of the scroll value are not equal to zero. If you observe the column from plane A which immediately comes after the last window column, you can see how the VDP fetches the wrong name table attributes from the next column over.
Here's a shot that clearly illustrates the intensity changes that are enabled in shadow / hilight mode. The statue's head is made of high priority background tiles, while the remainder of the display is composed of low priority tiles. You can see how even the transparent pixels that are part of the head object will 'lighten' the underlying tiles.
Finally, a picture from "Shadow of the Beast", which shows how the overscan area is affected by mid-frame changes to the corresponding border color entry in CRAM.