Joker and other villains defending Earth

I recall once watching a scene in which the Earth was being invaded by aliens or something. I think they were attacking as robots. And I think that I've seen Joker and other villains battling those aliens, defending the Earth. I am positively sure it was Batman I was watching, and I really think I saw Joker fighting those aliens.

But I can't seem to find the episode in which this happens. I can't even find any information regarding Joker doing this. Was I dreaming? Or is there really a scene (it may be in another animated series) in which this happens?