Tyranitar is the pseudo-legendary Pokemon introduced in Generation 2, ostensibly for the purpose of balancing the overpowered Psychic-types such as Mewtwo that made link battles in RBY so centralized. While its appearance is fearsome, it's actually more of a role player in GSC than some kind of sweeping behemoth. However, its impressive movepool, stat distribution, and unique typing do allow it to be very effective in a wide variety of niches for a team, both defensive and offensive. Its biggest selling point, in particular, is its niche as the only STAB Pursuit user that is reasonably sturdy (unlike Houndoom) and whose Pursuit is reasonably strong (unlike Umbreon). This allows it to check and KO prominent threats such as Gengar and Exeggutor which can otherwise create problems for teams with their combination of attacking prowess, status moves, and Explosion. Tyranitar might not be an unstoppable monster in GSC, but its unique talents make it one of the best Pokemon out there.
Defensive Tyranitar takes advantage of its solid defensive stats and unique defensive typing to act as a phazer for some of the most prominent threats in GSC. In particular, defensive Tyranitar is an effective phazer for Fire Blast Snorlax, Misdreavus, Jolteon, and Umbreon. Roar Tyranitar also helps to check more obscure threats such as Espeon, Muk, and Clefable.
The first two moves are a given; Rock Slide is Tyranitar's best STAB attack, whereas Roar defines the set. The last two moves could actually be filled in with several options. Curse is shown because it's common, and in conjunction with Roar, it allows Tyranitar to defend against threats such as Snorlax with Earthquake, and to possibly set up a late-game sweep. Rest keeps Tyranitar around for the long haul; without Rest, Tyranitar can eventually be worn away by Toxic, Spikes, and residual damage racked up as the battle wears on.
Other move options for the last two slots are too numerous to list. The best options are Fire Blast, Crunch, Earthquake, and Pursuit. Fire Blast lets Tyranitar threaten Exeggutor and Skarmory in the event that they might choose to stay in against Tyranitar. Crunch also lets Tyranitar hurt Exeggutor while giving it a more reliable way to hurt Ghost-types that choose to stay in, in addition to allowing it to force Miltank out via Special Defense drops and to prevent Starmie from switching in to spin away Spikes. Earthquake is good for neutral damage against most things that resist Rock, such as Machamp and Marowak, and also allows Tyranitar to 2HKO Muk and Nidoking. Pursuit is Tyranitar's best offensive move, allowing it to support its team by hitting Pokemon that switch out. It's great for sniping the Ghosts that wall non-Earthquake Snorlax, and is also good for chipping away at opponents such as Zapdos that will be inclined flee from Tyranitar. Pursuit is most effective when Tyranitar has an attacking move other than Rock Slide that allows it to force more switches.Team Options & Additional Comments >>>
Tyranitar can also ditch Roar and run an offensive set to take advantage of its diverse offensive movepool. DynamicPunch is the primary move that allows Tyranitar to act effectively as a mixed attacker. It allows Tyranitar to instantly threaten Snorlax and hurt Miltank and Umbreon on the switch. Without DynamicPunch, these common Pokemon wall Tyranitar perpetually.
Rock Slide is Tyranitar's strongest STAB move and allows Tyranitar to 2HKO Zapdos; this is key, as other mixed attackers such as Nidoking and Dragonite struggle mightily against Zapdos, only managing 3HKOs while Zapdos is able to hit them hard in return. Fire Blast allows Tyranitar to hurt Steel-types and Exeggutor. Pursuit is listed because, while it does little to improve Tyranitar's type coverage or ability to hurt switch-ins, it does allow Tyranitar to chip away at the things it is able to beat. STAB Pursuit is Tyranitar's biggest advantage over other mixed attackers; Tyranitar is walled by Suicune and Vaporeon regardless of its set, and as a result, using Pursuit to chip away at walls is how Tyranitar is able to consistently play an offensive role.
Other options in the non-DynamicPunch slots include Crunch, Earthquake, and Thunderbolt. Crunch allows Tyranitar to hurt Starmie and to deal better damage to Misdreavus, which might stay in fearing Pursuit. Earthquake allows Tyranitar to 2HKO Raikou, Muk, and Nidoking, all of which can otherwise easily take whatever Tyranitar dishes out. Both moves offer Tyranitar a decent attack to hurt what its other moves can't for at least neutral damage. Thunderbolt lets it flat-out beat Cloyster head-to-head and actually do some significant damage to Suicune as it switches in.
Tyranitar's moveset has a lot of room for customization. The moveset provided probably gives it the best chance for general success, but if you know specifically what you want out of Tyranitar, you can and should tack on the moves to let it fill those niches and hit the appropriate targets.Team Options & Additional Comments >>>
Tyranitar might also be able to effectively use a Curse + 3 attacks moveset. Something along the lines of Rock Slide / Earthquake / Fire Blast / Curse might make Tyranitar an effective Curse sweeper. However, due to the lack of a particularly strong physical STAB, this kind of set is mediocre on Tyranitar compared to other Curse sweepers such as Machamp and Rhydon, so it's usually best for Tyranitar to rely on STAB Pursuit and its mixed attacking movepool for offense. Surf and Ice Beam are other special attacking options on Tyranitar; they can help Tyranitar overcome its tendency to give Ground-types an easy switch-in opportunity, though generally these options are fairly mediocre. Tyranitar's set should focus on beating what it's supposed to, rather than spreading it too thin trying to help it beat what it isn't. Toxic is generally a mediocre move option as well, though it can be handy on Curse Tyranitar to help it force Miltank to waste Heal Bells, Umbreon to Rest, and to let it punish switch-ins such as Machamp and Marowak.
Some gimmicks that might prove effective on Tyranitar include AncientPower and Screech. The former might be good for across-the-board stat boosts, the latter for forcing switches and allowing Tyranitar to hurt foes such as Snorlax against which it would otherwise rely on the inaccurate DynamicPunch to do damage. Both are fairly poor move options, though, and should generally be avoided for more practical moves.
Checks and Counters
Tyranitar is hard walled by Suicune and Vaporeon no matter the set. Less common universal Tyranitar walls include Sleep Talk Machamp and Quagsire. Aside from the above, Miltank and Umbreon make solid checks, but fear DynamicPunch. Snorlax also becomes a check if Tyranitar isn't running DynamicPunch, though it needs to be wary of Rock Slide flinches. Marowak switches in well on Rock Slide and gets a free turn to attack once it does get in, but it can't afford to take too many Crunches or Earthquakes on the switch. Heracross switches in well, as it is decently defensive, usually has RestTalk, and forces Tyranitar out immediately, though it does not like switching in on Fire Blast and takes a considerable amount of damage from Rock Slide on the switch. Raikou, Nidoking, and Rhydon wall and set up counter-offensives against Tyranitar if it isn't using Earthquake. Steelix is a hard wall if Tyranitar isn't using Earthquake or Fire Blast; Forretress sets Spikes up in its face if it forgoes Fire Blast. Without Crunch, Starmie is a good Tyranitar counter. Without Thunderbolt, Tyranitar no longer threatens Cloyster with an attack that does 69%-80% in a single hit. This means that Cloyster can afford to stay in and set up Spikes, although it still isn't exactly a "counter" because it still takes a lot of damage (44%-52%) from Rock Slide, Crunch, or Fire Blast. Weirdly enough, Zapdos counters any Tyranitar that lacks Rock Slide. Even weirder is that Giga Drain Exeggutor counters Tyranitar if it lacks Fire Blast or Crunch.
Aside from the myriad set-dependent walls, Tyranitar is also effectively ruined by Toxic and passive damage. Unexpected things such as DynamicPunch from Gengar, Toxic from Fire Blast Snorlax, or Exeggutor using Giga Drain as Tyranitar switches in can all contribute to Tyranitar's untimely demise, so be sure to abuse them when you can if your team struggles against Tyranitar.