[Corel]

Slightly changing your above idea Meister, work in an enemy that the party have had combat difficulties with in the past before get completely smashed to pieces in the first round when trying conventional combat tactics against the boss. It might make them wise up not to do the same if they are given a strength comparison.

Then again this might remove the suspense of the boss reveal unless the enemies appear the same time you fight the boss. If you don't want to ruin the suprise for later you could have the party find the remains of said enemy killed in a way that players can piece together that something big and mean did it. Maybe a fragmented message/journal entry they could read?

It'll either teach them to run or fight outside the box; either one would be enjoyable I think.