Can Eldritch Poisoner take the Mutagen discovery?

[Quintain]

See subject. The class ability is replaced by archetype abilities (sneak attack), but can the discovery be taken as a token replacement?

[Eviljames]

That's pretty much what the discovery is for. So unless something in archetype specifically forbids it (as with the Promethean Alchemist) You can take the Mutagen discovery when you get a new discovery.