Thundurus-Incarnate Duo Guide
Unfortunately, Thundurus is one of the few Pokemon that lost the Gen 5 movepool lottery. Thundurus' best Electric-type moveset is Thunder Shock/Thunder; despite having much higher offensive stats than Raikou, Thunder is such a bad move that Thundurus-I lands just above Jolteon in performance. Furthermore, Thundurus-Incarnate is outclassed by its own alternate form, Thundurus-Therian; they have the exact same moves, but Thundurus-T's extremely high Base 295 Attack allows its performance to surpass Zapdos, falling just short of Raikou's.
As it stands now, Thundurus-I may not be very useful, but Thundurus-T is a Pokemon with a very high ceiling, and the two forms (should) share Candy. If Thundurus-T ever gets better Electric-type moves in the future, it will quickly surpass Raikou and Electivire and claim the spot of #2 Electric-type (behind only the unreleased Zekrom).
The Thundurus-I duo is fairly restrictive in terms of what Pokemon are viable, but the actual fight itself is quite easy due to how insanely powerful Rampardos is.
- Thunder Shock and Astonish are roughly equal in difficulty. Thunder Shock is boosted by STAB, but Mamoswine and Rhyperior sport Immunity-level resistances to Electric, making Thunder Shock much easier to face if you're using those 2.
- Brick Break comes out very frequently and hits both Rock- and Ice-types for super effective damage, making it the hardest Charge Move to face. However, its Base Power is very low, and even Rampardos can survive a Brick Break and instantly use its own Charge Move.
- Thunder hits decently hard and is difficult to dodge; however, Mamoswine and Rhyperior have no problems absorbing Thunders, making this an easier moveset to face than Brick Break.
- Crunch has good neutral coverage and comes out frequently due to being a 3-Bar move; however, it lacks STAB and is not particularly lethal. If you're using primarily Rampardos, Crunch will be the easiest moveset to go against.
- Thunder Punch is boosted by STAB and comes out frequently, but its Base Power is low, and it is 4x resisted by Mamoswine and Rhyperior, making this the easiest Charge Move to go against if you're using primarily those 2.
- Snow boosts the power of your Ice-type attacks, making the duo much easier if you're using Ice-types.
- Partly Cloudy boosts the power of your Rock-type attacks, making the duo much easier if you're using Rock-types.
- Rain boosts the power of Thundurus' Electric-type attacks. Under Rain, Thunder hits much harder, and Rampardos becomes non-viable against Thunder if you don't dodge it. If you do dodge Thunders, Rampardos is still the best counter.
Viable Counters
Minimum viable levels assume Best Friends, no Weather, no Dodging.
Italics indicate a Legacy move.
Rampardos and Mamoswine are significantly above the rest in performance; the more high-level Rampardos and Mamoswine you have, the easier this fight will be.
Level 40 Rampardos wins in ~240 seconds on average; Level 40 Mamoswine wins in ~260 seconds.
The next-best option after Mamoswine, Tyranitar, wins in ~280 seconds on average, out of the given 300 seconds.
Level 40 Psycho Cut/Ice Beam Mewtwo falls a little short of duo-viability on its own, but if you have enough Rampardos and Mamoswine carrying, you can afford to slot in a few Mewtwos without causing the run to fail.
Against Crunch, Level 40 Glaceon and Rhyperior fall a little short of duo-viability on their own; again, with enough Rampardos and Mamoswine doing the heavy lifting, you can afford to slot in a couple Glaceon and Rhyperior.
Against Thunder, Level 40 Weavile falls a little short of duo-viability on its own, but can be slotted in if your other Pokemon are strong enough to get you ahead of the timer.
If you're using primarily Rampardos, you will probably have to relobby twice; Rampardos faints an average of 26 times against Thunder, or 13 faints per trainer. Dodging some (but not all) Thunders will allow you to avoid a 2nd relobby without sacrificing too much DPS.
Against Brick Break, Level 40 Rhyperior, Glaceon, and Confusion/Ice Beam Mewtwo fall a little short of duo-viability on their own. The more high-level Rampardos and Mamoswine you have, the more safely you can slot in Rhyperior, Glaceon, or Mewtwo without sabotaging the run.