Originally for April Fools, there was originally a level set in an icey inviroment simply called "Ice Level" for the game. It is still in the game, but nothing like what it was originally like.
Going into the Lawnstrings folder reveals there were zombies called "Dog Walking Zombie" and "Propeller Zombie". The December 2nd, 2008 prototype contains their sprites.
Most insane of them all, though, is that there are a whopping 21 unused minigames in the game, 20 of them with their own unused page, the Limbo Page.
In October 2021, a two beta builds were released. The December 2nd, 2008 one (dated 5 months before the final game) which interestingly used one of Plants Vs. Zombies's known working titles, Bloom and Doom. The second one, dated Feburary 17th, 2009 was a more finalized build that used the final game's name but still has a few differences (like an earlier logo). These list of differences mainly apply to the earlier December prototype.
Many plants behaved differently at this point in the game's development:
Tangle Kelps can capture zombies before they enter the pool.
Zombies take damage when eating Torchwoods, giving Torchwoods even more utility. It's worth noting that Torchwood would finally gain this ability back in the sequel.
Several layout differences in most minigames and stages.
Crazy Dave's lines were not finalized yet. Some stages has him saying simple, generic lines clearly intended as a placeholder or had different wording.
An earlier design for Crazy Dave is present in the files, where he had longer ears and a different pan on his head.
Music was also not finalized yet. This was during a period of the game where its audio was making a transition from streamed audio in .mp3 format to music played in the .mo3 tracker format present in the final game. Plenty of tracks also used their versions from the Plants vs. Zombies Original Soundtrack among several other differences.
Several placeholder sprites drawn by Plants vs Zombies creator, George Fan before they were redone by Rich Werner, are present. Several unused zombie types are present, like the "Dog Walking Zombie" and "Propeller Zombie" mentioned in the final game's files.
There are a few Scrapped plants that goes unused but are still spawnable and fully functional:
"Ice Cabbage" (no relation to the one from the sequel). Works similarly to Ice Lettuce and is possibly an earlier version of him.
"Stinger" a plant that fires spikes towards flying zombies (though its tooltips mention it being able to shoot bees), it is able to be placed on top of other plants. Was reworked in to Cactus.
"Time Stopper", a plant that upon use, stops time for three seconds and while freezing time, refreshes the player's seed packet cooldown.
An early version of Cherry Bomb with a placeholder spriteset that works identically to the final Cherry Bomb, but hovers in the air and is attachable to other plants.
A plant that upon placement spawns a seed packet on top of itself that cycles between multiple different, plantable seeds.
A visible squirrel is present in a scrapped-in-the-final minigame appropriately titled, Squirrel.
In 2015, it was reported that Dreamworks Animation was developing a movie adaptation of the game that was to be directed by The LEGO Movie producer Roy Lee. Concept art for the film can be found online, but by 2022, it was ultimately confirmed that the project had been scrapped.
There was a planned stage called Time Twister. It was eventually incorporated into a Pinata Party event, with its own premium plant, the Wasabi Whip.
Far Future was going to have a future Crazy Dave. The extra levels of Far Future was also planned to have an upgrade to the Shield Zombie, whose forcefield could cover five lanes at once.
There were gravestones and minecarts for Pirate Seas and Far Future, and Wild West for the former and Ancient Egypt for the latter.
Scaredy-shroom was going to appear in Dark Ages, but was removed for unknown reasons. Possibly because of balance issues, because mushrooms don't have to be woken up anymore. It was finally added much later as a premium plant.
A plant called Burnadenote based on Burnet was implemented into the game but has no proper graphics, instead using Iceberg Lettuce's. When a zombie (including Gargantuars and minibosses) touched it, the zombie would get knocked back, start flashing for a while, then explode in a 3x3 area for damage equal to its health.
