Only the obvious one: Getting a Dragonite with Meteor. Of course, the announcement of the event caught me with exactly 1(!) Dratini candy. Plus one Dratini and one Dragonair I might send into the Candy Factory. I run my Dragonite as buddy now, but I won't be walking 500 km in the next few days. In a pinch I could throw in three rare candy.
What this comes down to is simple: I hope that on Community Day Dratinies will swarm like Pikachus did last month. In this case it should be possible to catch one every ten minutes. Pineaping everything, and collecting 124 candies within three hours is within reach.