Originally posted by Shaken_Widow:

not a bug, progression tracks to new worlds.

even though you didn't kill the elder on that world, the game recognizes that you were part of a world that had, and therefore have the ability to reach the next biome which makes those attacks happen.

this is why you don't bring a whelp to your friends server unless you're planning on making it your base server, only bring your chads over for parties.

Do you mean newly created worlds AFTER having joined someone that killed a boss?

I have killed the Elder in another world where I play, and yet when I return to my original world, I only get the Forest Moves as a raid. So I'm not exactly sure what triggers it from what you said.

I do not carry the drops from the Elder in my original world if that makes a difference.