That Ground subtype was incredible. Most folks have a thunder type to take care of water types, but if you're packing a Quagsire, the other guy's thunder type is in trouble. Ground type leaves you immune, and Earthquake lets you make short work of the thunder type. I seem to recall that I would usually have a grass type move on one of my Pokemon, or if I didn't just not worry about type effectiveness and bring out something that could deal heavy neutral damage and absorb Quagsire's attacks.