will it go to -kg or 0 kg?
Mew's weight is 8.8 lbs/4.0 kg. Automize lowers the user's weight by 220 lbs/100 kg. Automize cannot make the user's weight lower than 0.1 kg/0.2 lbs because lowering the user's weight to 0 or below introduces potiental danger to the game's calculation code and freezes the game. This is why nothing can have 0 HP/Atk/Def etc.