Unless you want to duo Aggron, then I would say 3 are very handy.
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I like having as many as possible for fighting gyms to make healing more efficient, but 2-3 is fine.
For duoing Tyranitar, you want a complete team of 6 Machamp/Hariyama.
For possible upcoming Regi raids, you want as many as your team has slots after putting in the applicable legendaries first.
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> For duoing Tyranitar, you want a complete team of 6 Machamp/Hariyama.
With weather boost you only need 4-5 with some dodging, without boost I doubt it's possible with hariyamas.
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6 Machamps would be fine...
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I guess I’ll have to do more solo Machamps in cloudy weather.
Edit: Cloudy weather to save 31k dust and 28 candy per champ. And Machops aren’t that common here too, not so easy to just find a high level boosted one, especially without trackers.