Do you mean, as in movesets?
Because if so, there are no four moves that can cover all 18 types. However, there are three types of movesets that can cover a whopping 14 types:
Ice, Fighting, Ground, Flying
Ice, Fighting, Ground, Grass
Ice, Fighting, Ground, Dark
Ice, Fighting and Ground together can super effectively hit 13 types, so that may be a good way to go if you want a very super effective moveset.
Hope I helped. :)
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