Angry Birds (NES, 2013)
Also known as: Super Angry Birds
This game has unused graphics.
The 2013 NES Angry Birds is a surprisingly good bootleg port of the homebrew Genesis demake of the mobile phone game, decidedly blowing the low-quality 2012 Nice Code port out of the water. Rare for an NES game, nearly all of the audio (the sole exception being the sound for selecting menu items) is stored as DPCM samples, all taken from the original game.
There's a few missing things (see below) and the physics are slightly off, but otherwise it's pretty faithful.
Buttons used on the end-of-level screen shown after losing and winning in the original game. This version scraps that screen in favor of writing "WIN" or "LOSE" across the screen in white 8×8 tiles, likely to save space.
Can you use the blue bird with some hacking?
Strangely, the blue bird is the only character that isn't used in any level whatsoever.