All challengers you face in battle (except Fredbear, Springbonnie, the balloon siblings, and the Puppet) come from an alternate timeline because of the flipside fracturing, leaking into other worlds.

In their point of view, they’ve been thrown into a drastically different environment, and now have to defend themselves against weird enemies using even weirder powers they’ve suddenly developed.

Which is the reason they attack the player’s party when found. They think you’re a danger to them.

Urrrghrhrhrhggh now I have the urge to go into horrible detail about every character and their lore-