I found out the other day that Chiron (the kind of not really super-centaur) was a son of Cronus. This is important because it puts Chiron on approximately the same scale of immortality as the Olympians. (On his mother’s side, Chiron is Athena’s cousin.)
And that matters because the Hydra’s poison affected him. Which means there’s a decent chance it could affect his half-siblings and cousins. Incidentally, the Hydra has an immortal head buried beneath a clearly marked monument on the road between two known cities.
Now, I’m not saying you should go dig it up and use it to poison weapons to use against the gods. Even if it puts them in such unbearable pain that they give up their immortality and voluntarily die, leaving you in charge of the universe.
And I’m not saying that all conventionally attractive people should carry a vial of Hydra poison around to retaliate just in case they can’t run from Apollo fast enough.
And I’m not saying you should ask your loved ones to put a vial under your tongue with or instead of the coin so you can fight your way out of the underworld before Persephone dissolves your mind.
And I’m not saying you should threaten the Hesperides with it until they give you a golden apple and make you immortal.
All I’m saying is hey, isn’t it interesting that there exists a thing that’s probably capable of harming the gods themselves, and isn’t it interesting that everyone knows exactly where to find it?