Game bugs

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.
Akumajou Densetsu	When a player enters the door, the game screen will bump up and down by 1 pixel.
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.
Donald Land	When the player progresses too quickly by boosting off of apples, the background loads fall behind and the scroll seam becomes visible.
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 II, III	The status bar suddenly change colors, sometimes when scrolling vertically it shows incorrectly for a couple of frames.
Hebereke	After switching to the password screen from the title screen, and when you return to the title screen to exit from the password screen, the triangle wave part is causing the glitch.
	When a player has contact with HUD, it caused the glitch that HUD disappears.
Hottarman no Chitei Tanken	During the game, when it caused a deceleration in when you are using a lot of heavy sprite, sometimes caused by a glitch in the scroll on the game suddenly it is paused and garbage sprites.
Kirby's Adventure	When Kirby of copy capability has changed, it attributed the icon flickers glitch representing the Kirby of the state, which is displayed in the status bar.
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.
Panic Restaurant	The in-game status bar, always bump up by 1 pixel.
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. You probably want to prevent impossible controller input by default in an emulator, but have an option to allow it for those feeling experimental.

• In Zelda II: The Adventure of Link, Link can gain tremendous speed when pressing left+right.
• In Spy vs. Spy, the character turns into an airplane when pressing left+right.
• In 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.

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).