Due to the way critical hits are calculated in Generation 1 of Pokémon, a move used by a level 0 Pokémon* will deal exactly the same damage regardless of whether it criticals or not. (It is possible to obtain level 0 Pokémon: Catch a Pokémon above level 100 using the Old Man glitch, then feed it Rare Candies until it gets to level 255. Giving it one more will cause it to underflow to level 0.)