Game bugs

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Listed are games that have been tested on NES or Famicom hardware and verified to look wrong or odd, due to things like NES hardware limitations or programming errors. Refer to this if you're developing an emulator and find a game that looks wrong, before you look for a problem in your emulator. If you are attempting to give your emulator "bug for bug" compatibility, you'll want to make sure that these glitches appear the same in your emulator as they do on the NES.

This is an incomplete list that concentrates on commercial games. For a list of homebrew programs that don't work on the NES, or which have glitches on the NES, see Program Compatibility. Sometimes, a bug slips into a game to make it rely on less-than-intentional features of the hardware; for those, see Tricky-to-emulate games.

Game Problem Screenshot
The Addams Family The in-game status bar occasionally bumps vertically by 1 pixel, caused by non-solid background pixels overlapping the sprite zero that is used for the status bar split.
Armadillo The in-game status bar occasionally bumps vertically by 1 pixel. This game also often suffers from slowdown.
Castlevania The PRG 0 version sometimes freezes right before the Grim Reaper. (Fixed in PRG 1 and PAL)
Castlevania II - Simon's Quest Sometimes incorrect tiles are shown on the playfield.
Castlevania III - Dracula's Curse The DMC channel in music sometimes mutes.
When pressing the 'B' button at the exact time as Trevor falls off a block, you hear the whip sound, but Trevor doesn't attack.
Commando Many numerous bugs that may seem as emulator glitches, but are normal operation.
Crystalis The scanline above the status bar and above text boxes looks wrong.
Double Dragon A garbage sprite can be seen on the lower right of the game screen.
The screen will sometimes shake vertically on heavy sprite usage.
Double Dragon 2 The status bar suddenly change colors, sometimes when scrolling vertically it shows incorrectly for a couple of frames.
Legend of Zelda The screen "jumps" off 2 pixels at the start and end of vertical fast scrolling
Mega Man 3 On the boss select screen, the scanline above Shadow Man looks wrong.
The first scanline of the menu is glitched.
Mega Man 5 In Gyro Man's stage, inside the two elevators, the floor moves up by a few pixels when the elevator goes up, and move back down when the screen is fast-scrolled.
Rad Racer Steer to the far left, and a background scanline will be seen on the road.
Star Tropics The island map music (NSF track 1) has a problem with the second square channel: it is intermittently silent or playing the wrong notes.
Super Mario Bros. The status bar shakes horizontally on heavy sprite usage and the music slows down. This can be seen especially in worlds 6-4, 7-4 and 8-4, where the large number of hammer objects created by Bowser's code causes the processing time to overshoot a frame. NMIs are disabled on entry to the NMI code and only reenabled when the CPU is "idle", thus when the overshoot occurs, the CPU "misses" a frame, causing general slowdown and status bar shakiness.
At various parts of 1-2, in certain CPU/PPU alignments, a single scanline gets glitched. This is caused by writing $2000 to reenable NMI at the exact end of the previous scanline, causing the PPU to begin that scanline from the first nametable instead of the second.
Super Mario Bros. 3 (U) The first scanline after a scroll split is glitched. This shows up as garbage above the left side of the status bar and as incorrectly scrolled lines in the "spade" (not N-spade) bonus game.
Note blocks containing items become squarer for a second while the item is popping out. (This is an artifact of the sprite priority exploit that it uses.)
If a Hammer Bros. battle ends precisely when a note is starting, the note will freeze on an incorrect duty cycle.
Big fat attribute glitch on the right side of most levels, because this game uses horizontal scrolling with horizontal mirroring.
Ironsword: Wizards and Warriors II Noise channel doesn't work properly, sometimes plays longer notes and sometimes mutes.

"Impossible" controller input

Many games do weird and buggy things when button combinations that would be impossible (or at least very hard) to input on a real controller are pressed. This comprises pressing left+right and up+down simultaneously. Prominent examples include Zelda 2 (Link can gain tremendous speed when pressing left+right), Spy vs Spy (the character turns into an airplane when pressing left+right), and Battletoads (pressing up+down in the vertical tunnel level kills the player instantly. Battletoads also seems to have more obscure and possibly game-breaking behavior related to pressing left+right in certain spots). You probably want to prevent impossible controller input by default in an emulator, but have an option to allow it for those feeling experimental.

Overscan ugliness

Some games display junk tiles in the overscan area, which is usually not seen (or is at least partially obstructed) on real TV sets. Examples include the NTSC versions of Metal Gear (seen e.g. in the jungle area when gameplay starts) and Solstice (on the title screen).