While often finding himself in the shadow of his already uncommon Incarnate forme, Thundurus-T is by no means something to take lightly, even in the Ubers tier. Easily the most noticeable of all his traits is his incredible Special Attack stat, which gives him the single most powerful Thunder in the game excluding the more-or-less irrelevant Analytic Magnezone, a feat that is not to be underestimated as Thunder is a very potent move in the Ubers tier. His speed stat of 101 isn't bad either, allowing him to outspeed the plethora of Base 90s and 95s. Volt Absorb and his Ground immunity give him plenty of opportunities to switch in and wreak havoc. Access to two great setup moves, Nasty Plot and Agility, only further prove how threatening he can become.
Unfortunately, several shortcomings hold Thundurus-T back from becoming a top-tier threat. The biggest problem isn't exactly a flaw Thundurus-T himself has, but rather the existence of Thundurus, which gives Thundurus-T huge competition thanks to the former's better Speed and access to an amazing ability in Prankster, albeit at the cost of some Special Attack. Zekrom also provides competition, due to having a Dragon typing, more mixed offenses, and much better bulk. Speaking of bulk, Thundurus-T has a major lack of it, meaning any decently powerful attack is likely to KO him, as well as an undesirable Stealth Rock weakness. Despite getting nearly perfect coverage with Focus Blast and Hidden Power Ice alongside Thunder, Focus Blast is rather inaccurate and Hidden Power Ice is a very weak move in the Ubers tier, so he can be walled relatively easily. Finally, Thundurus-T's speed, while decent, isn't quite good enough to outspeed threats such as Arceus, Latias, Mewtwo, and Darkrai, as well as the plethora of weather abusers and Choice Scarf users, so he will often find himself getting revenge killed without much trouble. Regardless, Thundurus-T access to one of the strongest Thunders in the game and two great immunities grant him a lease of life in Ubers. If you don't use him to his strengths, however, you'll find there are other Pokemon more suited for your team.
If you intend to use Thundurus-T in Ubers, this is by far the best set to use. Between having a good speed tier, a high Special Attack stat, and not really minding taking recoil considering how frail he already is, Thundurus-T makes a great Life Orb attacker. Thunder is simply non-negotiable for the choice of STAB move. Considering how prevalent rain is, which gives it perfect accuracy, as well as its high Base Power and chance of paralysis, the fact that Thundurus-T gets one of the strongest Thunder in the game only makes it all the more appealing. Although Focus Blast has very shaky accuracy, it is absolutely necessary in order to solve Thundurus-T's issues against Pokemon such as Excadrill, Ferrothorn, Tyranitar, and the Kyurem formes.
The third slot is where it starts to get tricky. Volt Switch is usually the preferred option, as it allows Thundurus-T to scout switch-ins which he won't be able to fight normally while still dealing a sizable amount of damage. Nasty Plot is a more direct approach to dealing with counters by allowing Thundurus-T to boost his offenses while your opponent switches in a counter, giving the strength he needs to power through said would-be counter. Do be aware that Nasty Plot should only be used if you need to break through walls; it should not be used to sweep. The final slot really depends on what you are running in the third slot. Grass Knot may seem like an odd choice due to providing only a small amount of additional coverage, but it allows Thundurus-T to OHKO Groudon and 2HKO Ground Arceus, both of which can easily stop Thundurus-T from using Volt Switch. The lack of coverage against some Dragons and Arceus formes isn't really a deal breaker as Thundurus-T can just Volt Switch out of such threats, and he shouldn't be picking a fight with most of them in the first place. If you intend to use Nasty Plot, however, then Hidden Power Ice will give better overall coverage against some of the slower Dragons such as Giratina that would otherwise wall Thundurus-T, and after a boost he can do more damage to Groudon and Ground Arceus than an unboosted Grass Knot.Team Options & Additional Comments >>>
Unfortunately, Thundurus-T has a relatively shallow movepool, but there are still some other usable options. Perhaps the next best idea after the Life Orb set would be a Choice Scarf set. By equipping him with a Choice Scarf, Thundurus-T gains a substantial amount of Speed, enough to outspeed the entire unboosted metagame save for Deoxys-S. He can use Volt Switch early-game to rack up damage and scout and then revenge kill or clean up late-game using Thundurus-T's great coverage. Unfortunately, being locked into Volt Switch is not really a good thing considering how incredibly common Groudon is, and Focus Blast and Hidden Power Ice aren't exactly good moves to be locked into either, not to mention he loses out on a substantial amount of power without Life Orb and will often find himself outclassed by other Choice Scarf users such as Palkia. For similar reasons, a Choice Specs set is also not recommended. An Expert Belt set is always an option but Choice Thundurus-T is rather uncommon so bluffing a Choice set is rather pointless. The lack of power from the Life Orb set and the lack of Speed from the Choice Scarf set make it all the more useless.
A stallbreaker set utilizing Nasty Plot and Substitute is also an option. Unfortunately, Thundurus-T seriously lacks the bulk to pull off such a set, as almost every Pokemon is capable of breaking his Substitute or phazing him. This job is best left to bulky SubCM users such as Giratina-O. Even Thundurus can pull such a set off better thanks to his access to Prankster Substitutes. Thunderbolt can be used instead of Thunder if one doesn't have access to rain, but because rain is so omnipresent in Ubers, plus the higher power and paralysis chance, there really isn't much of a reason not to use Thunder over Thunderbolt. He also has a decent Attack stat, and while his physical movepool is rather barren, he does get Superpower, which, with a Life Orb and without investment, has a good chance of 2HKOing Blissey and, after Stealth Rock, Chansey, and can OHKO Tyranitar. He also gets Crunch, which 2HKOes Latias and Latios after Stealth Rock given the same amount of investment and Life Orb. Thundurus-T also has a few support options in Thunder Wave and Taunt, but this is best left to Thundurus, who has access to Prankster which gives him priority in using these same support moves.
Checks and Counters
Outright countering Thundurus-T is rather difficult. This is because he is capable of simply scouting switch-ins with Volt Switch or U-turn, boosting with Nasty Plot, and launching devastating Thunders that also can paralyze. Regardless, there are plenty of ways to bring him to his knees. By placing Stealth Rock on the field, Thundurus-T will quickly build up residual damage from Life Orb recoil and switching out with Volt Switch or otherwise.
Outside of this, there are two real ways of taking on Thundurus-T. The first way is using a Pokemon that can sponge his attacks and KO or cripple him in some way, as even with a Nasty Plot boost some Pokemon are able to avoid an OHKO from his attacks. Latias and Latios do not care about anything that he can do besides a boosted Hidden Power Ice and the rare U-turn and can proceed to set up Calm Mind or simply outspeed and KO with Draco Meteor. Bulky Arceus formes also have no trouble in taking on Thundurus-T assuming they resist or are immune to Thunder. Like the Lati twins, they too are often able to outspeed and KO Thundurus-T. Ground Arceus in particular can stop him from scouting with Volt Switch and is outright immune to Thunder, but must watch out for Grass Knot. Blissey and Chansey laugh at his attempts at dealing damage, although they cannot do much in return. Other bulky Ground-types such as Groudon and Excadrill can negate his Volt Switch, but both have to watch out for Grass Knot and Focus Blast, respectively. Bulky Dragon-types in general are decent checks, including Reshiram, Zekrom, the Kyurem formes, and Dialga, though Kyurem-W and Dialga both need to be wary of Focus Blast and Zekrom needs to watch out for Hidden Power Ice.
Alternatively Thundurus-T can be taken out by simply revenge killing him. This is actually rather simple as his Speed tier, while good, leaves a lot to be desired. The aforementioned Latios, Latias, and Arceus, as well as Thundurus, Garchomp, Darkrai, Mewtwo, Deoxys-A, and every relevant Choice Scarf user in Ubers. Thundurus-T is also frail enough to be picked off with priority. Unboosted ExtremeSpeed from Extreme Killer Arceus is already a 2HKO and Thundurus-T fails to OHKO in return. The simple fact that Thundurus-T is really frail means that any moderately powerful attack that lands a hit will either seriously cripple or KO him.