Rock/Steel/Ground probably. I'd make sure to use a wide range though. Like:
Tyranitar
Metagross
Flygon
Rhydon
Aggron
Skarmory or Dugtrio
The total amount of types here would be: Rock, Dark, Steel, Psychic, Ground, Dragon and Flying if I choose Skarmory. Not to mention that these pok�mon can learn (overall) at least one move from every single type (all six pok�mon combined I mean).
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