If we're talking about food, Rainbow Dash's name makes me wonder if her mother is Mrs. Dash... wink
But seriously... Discord... In terms of what we've seen in canon, what we need is something that starts off seemingly harmless, but possibly enjoyable if you can look past the "what-in-Equestria-is-going-on" factor, but then becoming less and less pleasant until it finally kills you (if the stained glass is a true depiction of what he did, anyway).
So maybe an Everlasting Gobstopper specially made so that the flavors run like that, and then the center is a noxious poison.
There is no honor in using poison. If you must kill your enemy, you let him die knowing the face of his killer. THAT is the Klingon way. emotion_donotwant
Now, for the matter of food. I am...disappointed with some of your ideas as to what I would be.
lolwat? Um... this is a weird question. I think of flan when I think of Rarity I guess. Fluttershy makes me think of Elven bread from LOTR. Twilight makes me think of something powdered. Like pixie sticks.