ONLY DELETE ONE POKEMON, NOT TWO, NOT THREE, NOT FOUR. PLEASE GUYS. :(
Let's say GameFreak was going to opt for 155 Pokemon, to make the total amount Unova introduces to a nicer amount (or whatever reason you can think of!) This means one Pokemon has to be deleted from Unova's history - forever! You, as head of GF, get to make the decision (altho I'm sure that isn't what'd really happen, nevertheless...) Which Pokemon do you choose to remove from the UnovaDex? You must give reasoning, and it can't be just because you find it ugly, or something. Does it not fit in well? Does it appear too much? Was its design lacking in comparison? Was the idea behind it boring? etc.
Now make your decision :) Just don't answer the questions as a list!!