Tyranitar

Tyranitar is the defining Pokemon of ADV OU. First, its ability Sand Stream alone tremendously shapes the strategies and team choices in the metagame. By damaging and nullifying Leftovers on non-Steel-, Ground-, and Rock-types, sand shifts similar roles towards Pokemon that are immune to or more robust under sand. Swampert more reliably checks physical threats than Suicune despite worse stats; Claydol is the preferred spinner over Starmie even with its middling Speed and offensive presence; Blissey's extreme special bulk keeps it around a lot longer under sand than Celebi, and it forms part of the Skarmory + Blissey core so frequently used on defensive teams with Tyranitar. As a result, sand defines one of the most prominent defensive archetypes in the metagame: Toxic + Sandstorm + Spikes (TSS). As an offensive tool, sand makes damage stick, greatly neutering the effectiveness of threatening setup sweepers like Suicune and Snorlax while also forcing frequent recovery from Celebi, Blissey, and Milotic. As a defensive tool, sand limits certain varieties of offense by placing Choice Band and Berry-focused Pokemon on a timer. Sand also provides a lot of information in battle, revealing the items on Pokemon like Salamence and Heracross and distinguishing Choice Band and Salac Berry sets from those running Leftovers. As a simulator mechanic, sand reveals the relative Speeds of the Pokemon on the field, dealing damage to the faster Pokemon first.

Sand isn’t enough for you? Tyranitar itself is a behemoth in battle; with a strong stat distribution and large movepool, it can fulfill a variety of roles on almost every team. The Dragon Dance set can act as a wallbreaker or sweeper; Pursuit threatens to punish not just Gengar but also other hovering threats such as Choice Band Salamence, Aerodactyl, Moltres, and Claydol; the mixed set dismantles TSS-style teams; the bulky physical attacker set exploits Spikes really well by forcing switches; the Choice Band set provides a lot of immediate firepower if supported well or accompanied by good predictions; and the SubPunch set gives added protection against status from Blissey and Snorlax and can be a great lure. While these sets are mostly offensive in nature, Tyranitar's typing and decent defensive stats also allow it to pivot in on Normal-, Fire-, Flying-, and Psychic-type moves, guarding the team against Snorlax, Moltres, Aerodactyl, Salamence, Celebi, and Jirachi.

While Tyranitar has an incredible number of strengths, it is not without weaknesses. It fails to outspeed just about every offensive Pokemon and even some defensive ones like Celebi without considerable Speed investment. Even with a Speed boost from Dragon Dance, it can be outsped by Dugtrio, Aerodactyl, Jolteon, and possibly Starmie. While its typing is mostly positive for it, the Water- and Ground-type weaknesses prevent it from staying in on bulky Water-types and allow it to be easily trapped by Dugtrio. In particular, teams that derive their value from Tyranitar through sand immunity usually leave themselves prone to offensive Water-types, as they usually rely on a single special wall as their Water-type check. Other weaknesses such as Fighting, Grass, and Steel allow many Pokemon to take out Tyranitar in up to two hits after some chip damage, and these attacks frequently come from Pokemon that Tyranitar is supposed to check or be able to do heavy damage to in the first place, like Salamence, Metagross, Gengar, offensive Jirachi, and Celebi. Keeping Tyranitar healthy enough to serve its purpose is key to using it successfully.