I was envisioning how I would have my current party encounter Kuxcoatl, and I was thinking somehow he would send them on to find some sort of item/device to appease his curiosity, and along the way through the adventure give them some way to booby-trap the thing he sent them looking for. The cursed item wouldn't kill the dragon, just make him vulnerable, and somehow let the party do some type of damage to him that would banish him from their plane. (since I have so little to work with right now, the adventurers are surely going to encounter him again and likely be pulled to his plane somehow). The other option for the party is just to seek to appease him and somehow garner some gift from him- which would trigger other great wyrms to somehow have their interest pulled to them sparking another encounter.
Something else that came to mind was making an actual battle similar in token to a JRPG where they battle just a part of the dragon whilst he is distracted by some other event going on, and somehow disabling it, either via interactions with the environment or just by attrition over a number of turns.