Here’s a mystery for you. Do you have any reasonable theories as to why every pokemon that can learn tms can also learn toxic? In the 1st generation games, when it was first given to you by Koga, he said it was some sort of secret technique that’s over 400 years old. Though I’m not sure what sort of ninja technique allows one to spew out a blob of incredibly poisonous goo, unless we’re getting into Naruto territory. It just kinda irks me is all.

Not really… I think you’re right to look to Koga’s description of Toxic; it is his signature move, after all.  The idea that ninjas use poison is also fairly uncontroversial.  Since it’s described as a ninja technique – that is, a technique used by human spies and assassins – I’d probably handwave it by saying that teaching Toxic to a Pokémon with no poison of its own involves teaching it to identify and gather parts of poisonous plants or mushrooms and somehow store them until they’re ready for use without actually suffering from their effects (maybe chewing two different components together creates the toxic effect, so you can keep them separate until the last minute and then spit them out as soon as they’re combined?).  I don’t know.  Something like that, anyway.  It probably varies from Pokémon to Pokémon.