From Bulbapedia, the community-driven Pokémon encyclopedia.
Like previous major releases, especially those that set a new generation, Pokémon Black and White went through multiple development stages, many of which included several elements that were eventually dropped or revised before the games' release. Some of these components can still be found within their internal data.
The prototype starter
The sprite on the starter selection screen for Tepig was different in some early videos. The prototype sprite had a more triangular hind foot, with only one of which shown, and had slightly different shading. Also, while selecting the starter, the other two starters were less darkened when compared to the final release.
Prototype sprites for Hilbert and Cheren were shown in an early video which was broadcasted on Pokémon Sunday. Although the difference for Cheren's sprite is only where his eyes face, Hilbert's sprite received a complete overhaul. A prototype sprite for Bianca, lacking her Xtransceiver, was shown in the early video footage that came with an issue of Dengeki Nintendo DS.
In Excadrill's first appearance in a promotional video, its stripes were mirrored. However, this was not long-lived, as it was changed to its current appearance in the next video.
Beta Cheren VS sprite.jpg
Cheren's prototype VS sprite
In some early footage of Route 4, 夢の跡地 Dreamyard can be heard playing instead of the correspondent seasonal variant of ４番道路 Route 4.
Some retailers in the United Kingdom (specifically GAME and Gamestation) had pre-release box art using the name Alleos for the region as opposed to its final English name, Unova. This name was also used at pre-release and post-release demo events in the United Kingdom.
There were many changes to Castelia City, where at least four different textures were shown before the final design. A few of these designs can be seen below.
Image released on April 15, 2010
Footage from the June 27, 2010 trailer that was broadcasted on Oha Suta
Image from a Pokemon.co.jp video
Image released on May 14, 2010
Another image from a Pokemon.co.jp video
On an early screenshot of within Skyarrow Bridge, a Backpacker can be seen, who was replaced with an Ace Trainer in the final release. However, in the final release version of B2/W2, the exact same spot is occupied by a female Backpacker, just like in the early screenshot for B/W. In addition, two images released of the Skyarrow Bridge depicted a slightly different skyline of Castelia City.
When buying items at a Pokémon Center, the part of the screen where the player can be seen is shown to rotate a bit.
Since the engine that powers the games is improved upon that of the Generation IV games, all items from Generation IV, including Poké Balls, key items and unused items, are present in the internal data, with the exception of HM07 and HM08, which are now blank space "?" items. However, most of these items are unobtainable. Other leftover items, like the God Stone, are specific to Pokémon Black and White and can be likewise obtained through modification of the saved game or cheating.
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If the player uses the "walk through walls" cheat, enters the P2 Laboratory and keeps walking down, there will be some leftover tables. (link)