Or alternatively, give them an uber powerful NPC, who gives them tactical advice, teaches them how to fight dragons, whittles down its hitpoints a bit and then gets eaten (not swallowed whole, chewed up and then swallowed)
This is flat-out bad advice. It feels contrived and makes the PCs feel worthless. If you do it badly, it'll break verisimilitude. If you're trying for any sort of seriousness at all, please, for the love of PunPun, don't do this.