Exeggutor or Alakazam probably. But I think Eggy has the higher ground with two resistances and Solar Beam, and a psychic fast move.
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Unless the Poliwrath is packing Ice Punch. In that case, Slowbro/king with Confusion/Psychic may actually be the safest option, though obviously not the fastest one.
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I have really a lot of double psychic Slowbros at 1.9k CP. Now I use them for my defensive team.
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Exeggutor, Lugia, Alakazam and Espeon seems the most powerful counters. Exeggutor resist both water and fighting, and Lugia resist fighting twice and have a gargantua def stats. I think Lugia is the best counter.
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Dragonite with Dragon Tail/Hurricane might also be good, plus it resists both water and fighting.. unless the Poliwrath has ice punch, then it would hurt quite a bit.
Once Zapdos is out, it's also a good counter as it resists fighting and has strong electric moves.
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Lugia with both Psychic movesets and Exegg with Psychic Fast / SoB