Edit - I see that Toujours already mentioned this, but I overlooked it, sorry!
While it might not really be a 'conspiracy', I'm extremely interested in the theory of Venomoth being switched with Butterfree.
If you look at Venonat and Butterfree, you'll notice that they share a huge amount of similarities. The eyes, for example, are both big and red, like bug eyes. The colour of both Pokémon is the same, purple. The antennae are also the same, as for the mouth, and the big feet, and claw like, tiny hands.
If you look at Metapod and Venomoth, you'll also spot similarities (though not as much as with Venonat and Butterfree, but still). Metapod and Venomoth have the same forehead structure, which is also on the head of Caterpie, only in a different form. The eyes of Caterpie and Metapod are also more similar to the eyes of Venomoth, than Butterfree.
An interesting thing to point out, is the sprites of these Pokémon from Pokémon Green version. You can see here below that Venonat and Butterfree look almost completely the same, apart from their own body structure and Butterfree's wings. Venonat is just a purple fuzzy ball, with all the features of Butterfree.
The theory is that in the first game, the editors messed up somehow and switched the sprites for Venomoth and Butterfree by accident, found out later about it when the game already released, and to cover up their mistake, they kept it that way and changed that to the official evolution lines. That means that Butterfree as of now, was actually meant to be 'Venomoth', and vice versa. This is supported by the fact that when you look at Venomoths wings, they look a lot like butterfly wings as well, so it wouldn't have been strange if Venomoth was actually supposed to be 'Butterfree'.
This is just something that interests me a lot, because you just can't get around the fact that Venonat and Butterfree look almost the same in their features, and the same goes for Metapod and Venomoth with the eyes and head structure. But we can never be sure about what the real reason for it was.