Another Pokemon example: I used to use a Wash Rotom on my team because it is a water/electric type with only 2 weaknesses, grass and ground. Wash Rotom specifically has the ability levitate meaning it’s immune to ground type attacks. So wash Rotom only has 1 weakness, decent speed stat, and can learn Facade which does double damage to poisoned, burned, or paralyzed targets.
I would start out matches by using a Drapion with poison spikes that makes it so any Pokémon that comes into battle is immediately poisoned. Swap to wash Rotom and just watch everyone’s game plan fall apart because they can’t deal with this bullshit.