I Was A Teenage Gary is an early Halloween episode of SpongeBob SquarePants that first aired on October 28, 1999. Many people that watched SpongeBob during the early 2000's have claimed to see the original airing of this episode and said there was a scene that involved Squidward transforming into a snail after he realizes the snail plasma needle injected into his nose. Many have criticized this scene for showing SpongeBob turning into a snail, but not Squidward. However, some say that out of the two transformations, Squidward's was the most frightening to watch.
There is plenty of evidence to showcase that this scene might be real. For instance, after Squidward notices the needle, there is a wipe transition rather than the normal bubble transition, leading some to believe that Nickelodeon had implemented the former transition in the episode for reruns instead of re-animating it with the bubble transition.
Another speculation of this is that in the Poland airings, they show this scene, but since Poland airings are very rare to find. YouTuber and Lost Media Contributor 404UsernameNotFound found a polish airing on a foreign website (Links below.) YouTuber 90sGiveMeGoosebumps uploaded a clip of the original airing of this episode on VHS, but others say that it might just be the first rerun of the episode.
This "deleted scene" is not shown on any DVD releases, so it's unknown if it actually exists, conclusively leaving only theories of this scene to actually exist. Someone YouTube uploaded the first airing of the episode And...it wasn't there
Edit: Lost Media Contributor 404UsernameNotFound found a polish dubbed full episode of this. The original link can be found here. (No viruses detected) He also has a Google Drive save of it for people who don't want to go to the ad-filled website.
Edit 2: There is even an English version. http://watchcartoonsonline.eu/watch/spongebob-squarepants-s1-ep13b-teenage-gary/
The existence is now confirmed to be fake.