keep yoda banned, despite the fact that he is indisputably the worst character in the game, for the following reasons.
there is a much smaller move list available for fighting him. this leads to matches being very homogeneous, and homogeneous matches are uninteresting for spectators. if we are trying to garner interest in tournaments and competitive play then we need to do what we can to keep matches interesting.
yoda is not only a terribly weak character, yoda is a terribly designed character as well. in the event that there is ever a sc5 i do not want to see another character that has yodaesque immunities in it. the best way to avoid seeing a yoda mark 2, is to show in no uncertain terms how much we hated his guts the first time around.
banning yoda is doing new players a favor. since yoda is not merely bad but actually orders of magnitude worse than any other character, if yoda is banned then new players wont pick him in tournaments and thus they will not get absolutely destroyed because he can never win anything.
banning yoda is doing a favor for other players too. playing against yoda is boring. really boring. if he is banned then maybe i wont see him as often.
in conclusion, yoda is a negative influence on the game. if the mythical patch 1.04 deleted the little green goblin from the game would you mourn his loss?
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the special characters are not fine. their inclusion does not add anything to the game but cosmetics, and in some cases an argument could be made that they are just better than their counterpart (ashlotte's much smaller hit box comes to mind). i would argue that their inclusion does not add to the game outside a measure of aesthetics and i can see no reason to risk adding some imbalance merely to accommodate aesthetics.
in retrospect that last paragraph should have been first, but i really hate yoda.