What's wrong with lightweight? Sure, you get knocked away a lot farther, but Pichu is much faster than most characters. Actually, because of that, Pichu's attacks damaging it don't even matter, because with that speed you'll be able to avoid most things.
Besides, Pichu only has like, four attacks that it damages itself with, and with one of them you can actually still use it without damaging yourself, if you do it a certain way. But it's not like you have to use any of those moves.
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