Since its Incarnate form is used almost exclusively as a bulky Thunder Wave user, Thundurus-T is what people think of when they hear "Offensive Thundurus". Sporting a staggering base 145 Special Attack, decent coverage and Speed, as well as a great defensive typing and ability, Thundurus-T was always destined for greatness. Although it does face some competition from the likes of Zapdos and Rotom-W for the role of bulky electric, mainly due to its reliance on Hidden Power for extra coverage, Thundurus-T has made a name for itself despite its late arrival.
Choice Thundurus-T is fairly one-dimensional. With its STAB Thunderbolt and Hidden Power backed by a Choice Specs boost, Thundurus-T is more than capable of ripping holes in the opponent's team, provided it doesn't get caught out with the wrong move in the wrong situation. Thunderbolt is self-explanatory, but Volt Switch might need more explanation, considering the rarity of such moves in VGC. The premise behind Volt Switch is this: although Thundurus-Therian hits hard, in a metagame where everything is either EVed to take Dragon Gem Draco Meteors, some Pokemon need softening up before Thundurus is ready to knock heads. Furthermore, Volt Switch hits almost as hard as Thunderbolt does, making it a safe move to throw out in the beginning of the game. The choice of Hidden Power largely depends on how well your team takes on Fighting-types or Dragon-types, but due to STAB, Hidden Power Flying is naturally the more powerful option. Hidden Power Ice, however, gives you the edge against other Thundurus-T that chose Hidden Power Flying, and it is powerful enough to OHKO Yache Berry Garchomp at about the same rate as Scald burns (and we all know how often that is), which is something normally only Ice-types such as Mamoswine and Abomasnow can claim to do. In the same situation, Garchomp cannot OHKO Thundurus-T without resorting to the inaccurate Stone Edge.
As for the third slot, Grass Knot is the best that Thundurus-T's rather shallow movepool has to offer, but it can be useful in situations where Thundurus-T is left alone against Tyranitar or Gastrodon. It might also be wise to study up on the weights of some Pokemon before haphazardly locking yourself into Grass Knot. A prime example is Rotom-W, which only takes about 25% from a 20 Base Power super effective Choice Specs-boosted Grass Knot. If you have trouble memorizing weights, pay attention to the 'slamming' animation that most Pokemon make when entering the field.
This analysis has so far listed a few examples of Thundurus-T's power. It should be noted, however, that those examples are the work of a Choice Specs boost, which means you won't be getting the same mileage out of Choice Scarf. Choice Scarf is still a great option though, as it outspeeds Choice Scarf Tyranitar and Landorus-T, Latios, neutral +1 Volcarona, and other such Pokemon that Thundurus-T might have interest in outspeeding. This makes Choice Scarf Thundurus-T most useful in revenge killing, especially if you have Fake Out users or Pokemon that can easily soften up the opposing team.Team Options & Additional Comments >>>
While lacking in Speed or attacking prowess, specially attacking Thundurus-T is unique in its versatility. Being able to switch between moves is incredibly useful, considering how Choice Specs or Choice Scarf Thundurus-T is easily walled should it lock itself into an unfavorable move. It also isn't forced to switch moves and has increased longevity thanks to Protect, which is useful to avoid double-targeting.
Even though this Thundurus-T is more versatile in its playstyle, its moveslots aren't very flexible. The standard Thunderbolt, Hidden Power, and Grass Knot core is hard to replace, as it is really all Thundurus-T needs in the first place. The question of which Hidden Power to use is the same as the Choice sets; do you want to hit Dragon- or Fighting-types? There is no wrong answer to this question because it depends largely on your team, so you might find yourself bouncing between the two in practice. Protect is almost non-negotiable, as one of the main draws for a non-Choice set is the ability to use it, but if you don’t feel the need for it, you can easily switch it with Volt Switch to make a miniature Choice set.Team Options & Additional Comments >>>
Thundurus-T has a few tricks up its cotton-candied sleeve, but unfortunately the vast majority of them are very situational. Flash Cannon is actually rather useful to hit both Abomasnow and Tyranitar super effectively, but it still can't KO either consistently, even with a Choice Specs boost. Focus Blast would be a great option for those two as well if it didn't have an atrocious 70% accuracy, which might seem like a fair trade, but in reality it isn't worth it because both Pokemon usually hold Focus Sashes or Chople Berries to mitigate their Fighting-type weakness. Superpower has more appealing accuracy and still has Thundurus-T's overlooked base 105 Attack to work off of, but requires investment to OHKO anything, and even then it's vulnerable to Intimidate Attack drops. Taunt and Nasty Plot can be useful in the special attacker set, where Grass Knot is used even less often. Taunt can shut down Trick Room or Amoonguss (since Thundurus-T can't OHKO specially defensive variants), which is actually very helpful, but is still a rather situational move especially considering how frail Thundurus-T is. Nasty Plot, when given a turn to set up, can mow down Pokemon that usually check it, such as Cresselia, Tyranitar, and Rotom-W, and OHKOes its bulky Incarnate counterpart. The problem lies with Thundurus-T actually getting the boost and staying alive afterwards after the opponent starts to focus fire on the suddenly very threatening Therian.
In terms of items other, the regular attacking Thundurus-T has a lot to choose from, including Focus Sash, Ice or Flying Gems, and Expert Belt. Focus Sash is attractive, but usually not worth the drop in power unless you're interested in OHKOing Terrakion or Landorus-T without having to lock Thundurus-T into Grass Knot or Hidden Power. Flying and Ice Gems provide a Specs-esque boost, but only to their respective Hidden Powers, which don't usually have much to gain from a Gem boost. Expert Belt can provide power and versatility, but more importantly it can bluff Choice items. Expert Belt requires a super effective hit however, and even when it does, it doesn't provide a boost like a Gem or Life Orb would, which means Thundurus-T might miss out on some KOs on Pokemon such as Metagross.
A bulkier EV spread might seem like a waste and overshadowed by Thundurus's bulky spreads, but can actually be useful against common attacks, especially if you're using Thundurus-T's excellent synergy with Water-types. A spread of 96 HP / 32 Def / 248 SpA / 8 SpD / 124 Spe allows Thundurus-T to survive attacks such as Bisharp's Dark Gem Sucker Punch and Timid Latios's non-Life Orb or Dragon Gem-boosted Draco Meteor, allowing Thundurus-T to actually KO the two or at least heavily damage them without having to worry about Speed or priority ruining its day. Of course, that spread is for Hidden Power Flying, so you should use 92 HP / 32 Def / 252 SpA / 4 SpD / 132 Spe when using Hidden Power Ice.
Checks and Counters
While Thundurus-T might be able to poke massive holes in your team, if you've EVed your Pokemon to take powerful Dragon Gem-boosted Draco Meteors, you've won half the battle already. Pokemon such as Cresselia and Tyranitar can already take such attacks and either OHKO Thundurus (you might want to Protect to rack up a turn of sandstorm damage to maximize your chances) or slow it down for other Pokemon to KO it. Simply outspeeding it and smacking it with a powerful STAB move is sometimes all it takes to quell the Thundur, which is precisely what Mamoswine, Terrakion, Choice Scarf Tyranitar and Weavile do from the start. Fast Draco Meteors are also great deterrents for Thundurus, and they mostly come from the likes of Latios or Kingdra in the rain. Kingdra can be especially dangerous because it's usually in a rain team's best interest to KO Thundurus as soon as possible. Choice Thundurus are easy to predict around if you have reason to believe it is in fact Choice-locked, as Thundurus has a tendency to lock itself into an undesirable move early-game. Pokemon that can take advantage of this misfortune are Gastrodon and Metagross, as well as just about every Pokemon previously mentioned. Trick Room is deadly with the right attackers, which more often than not, includes Tyranitar or Abomasnow, both of which obviously OHKO Thundurus-T with little hassle.
As far as counters go, Lanturn is the #1 anti-Thundurus-T Pokemon. Not only does it resist or is immune to every move Thundurus can throw at it (besides unorthodox options such as Focus Blast), Thundurus-T's Grass Knot only hits for 40 Base Power, which only pulls out a 4HKO, without even factoring in healing. With this extra time on its hands, Lanturn can casually slow Thundurus with Icy Wind or chip away at it with STAB Water-type moves or Ice Beam. Lanturn is also a potential problem for rain teams, but doesn't fare too well against other teams that happen to include Thundurus-T. Perhaps ironically, Hidden Power Flying Thundurus-T are susceptible to Thundurus-T that opt for Hidden Power Ice because Volt Absorb negates its primary STAB. Similarly, Hidden Power Flying Thundurus-T is also effectively walled by Jolteon, Zebstrika, Raichu, and sometimes Rhyperior, though all of these examples are hard to fit onto a team. Rotom-H is another great candidate, as it resists all of Thundurus's moves and can OHKO with Overheat or if in the rain, 2HKO with Hidden Power.