This fight would be absolutely rediculous, but I'm inspired by a reddit post about if all the pokemon could defeat 1 billion lions. A lot of pokemon would loose to a single lion but I think the really good ones would pull their weight. Even pikachu could probably zap hundreds to thousands to death. The problem is each one would have to kill well over a million on average before factoring in the ones who won't kill a single lion such as caterpie unless it got lucky while a lion was distracted and string shot him so he trips and breaks his neck, or something stupid.

You'd have to remove the legendaries and claim lions could hit ghost pokemon for the lions to have a chance though.