Super Mario Bros 3 did diagonal scrolling, which was not an intended feature of the hardware; it also used some careful timing to split the screen between the play area and the status area on the bottom.
Many console games reprogrammed or switched palettes partway through scanout to get more colors on the screen than normally possible; some did so with careful timing in the middle of horizontal scanlines. Emulators commonly don't implement this, because it adds significant overhead to the scanout fast-path. See the screenshot of Air Strike Patrol in http://arstechnica.com/gaming/2011/08/accuracy-takes-power-o... , where failing to emulate intra-scanline changes results in the plane's shadow disappearing, which is a critical gameplay component that makes it easier to aim.
While playing games using 8 bit NES cards powered by a stabiliser; if you increase and decrease the voltage alternatively very fast it would give you 30 lives in Super Contra.
