Garchomp
Much like in Gen 7 OU, Garchomp's most common set is its Stealth Rock+Z-move offensive set. Life Orb is also seen occasionally. However, while Garchomp is arguably better suited for offense, it can still work as a great physical tank.
Mega Garchomp
The Mega sees some sparse use as an offensive Stealth Rock user, but regular Garchomp is usually better since it has the ability to hold Z-moves and outspeed several Pokemon Megachomp can't. Now that it has gained Scale Shot, Mega Garchomp's role has shifted to become a dangerous sweeper.
Greninja
Protean Greninja's most common set is a more physically oriented Choice Scarfer with Ice Beam to threaten to KO the likes of Garchomp, Gliscor, and Landorus-Therian and set up Spikes to hurt would-be checks and counters and to make its U-turn more deadly. Outside of that, mixed Life Orb still sees some usage.
Ash-Greninja
Its role is pretty much unchanged since Gen 7; wallbreak, force things out, and use Spikes while the enemy switches to wear down its checks. Even its moveset hasn't had any significant changes.
Gliscor
Right now, the defensive set is seeing more use than the Swords Dance one. Since it has Poison Heal, the lack of a Rock weakness, generally positive matchups against non Hp Ice Landorus-T and most Heatran variants, and by technicality, a Knock off and status immunity, it can function as an effective bulky Defogger.
Tyranitar
Since Ttar has Pursuit in Nat Dex, its most common set is very similar to Gen 7's Choice Band set. Assault Vest sets are also good, however they see much less usage. Smooth Rock is seen on some dedicated Sand teams to support sand sweepers like Excadrill and Dracozolt. There's also the bulky Leftovers set from Gen 8 OU which is seen rarely because of the power of Banded Pursuit but still puts in some work.
