That sounds like a great idea!
It could be some kind of competitive cooperative boss battle - that's something that has existed in various mobile and other digital card games.
I might actually write a whole post with what it could look like, without having to change much at all from how Splinterlands already functions.
Well and it would be a great way to help increase everyone's knowledge of the lore. Could be splinter specific lore or it could be the lore for the editions. I have to imagine something like that would be on their road map since the lore is already written.