Aurorus is certainly an interesting concept and design for a fossil Pokemon. With a unique typing and access to some more uncommon abilities, it seems like an interesting choice to try on your team...until you get a good look at its stats and movepool. Aurorus has a typing that makes for a good STAB combo, especially if you add Earth Power for coverage. However, its stats are not sufficient to take advantage of its typing, and its poor speed and physical defense leave it vulnerable to six weaknesses, including 4x weaknesses to Steel and Fighting, and it has few resistances. Its Rock-type movepool is limited, too; the poor thing would have loved Power Gem, but you'll have to settle with AncientPower if you want a special Rock STAB. Still, with two solid abilities, a great HP stat, and some decent options on the special side, Aurorus can find itself a niche in competitive gameplay.
Littlefoot's Cooler Brother
Item: Choice Specs / Icy Rock
EVs/Nature: 252 SpA / 4 SpD / 252 Spe, Modest nature
Ability: Refrigerate / Snow Warning
- Hyper Voice / Blizzard
- Earth Power
- Freeze Dry
- AncientPower / Stealth Rock
This set is actually two NU sets rolled into one. The options before the slashes are one set, and after the slashes is another set, with the exception of the last moveslot. You can run a Refrigerate set for maximum damage with Choice Specs; this makes Aurorus hit quite hard and makes its coverage moves more intimidating. Alternatively, after the slashes we have a Hail set, which trades off raw damage for 100% accurate spammable Blizzards, with a small chance to freeze. Since this set uses Hail, it also breaks sashes and Sturdy. Using an Icy Rock keeps the Hail up as long as possible and keeps you from getting choice-locked into the wrong move. In either case, the idea here is to do a lot of damage and threaten some bulkier threats. In the last slot, AncientPower is a nice STAB option with a small chance to boost your stats, but Stealth Rock can be nice, and few hazard removers like switching into Aurorus. Other options that Aurorus can substitute into that last slot include Rock Tomb for speed control, or Dragon Tail / Roar or Frost Breath to deal with Calm Mind users.
Counterin Aurorus is, unfortunately, not all that difficult. All you really need is decent speed and attack and a good physical Fighting- or Steel-type move. In fact, you can scratch the speed if you have Mach Punch or Bullet Punch. Aurorus's special bulk, however, makes things like Flash Cannon and Focus Blast risky tactics; run some damage calcs if that's the best counter to Aurorus on your team. Defensive options are less effective, since Aurorus has some good coverage, but Hariyama does a good job taking hits from it and threatens back with its own STAB. Bulky Water and Steel types also perform well against Aurorus, resisting its favorite STAB moves and often not being threatened enough by its coverage. Note that Aurorus should not be used above maybe RU tier; beyond that, its weaknesses paired with its poor Speed and Defense will get it destroyed every time.
and I think Life Orb or Choice Specs are much better items since Aurorus could use as much of a boost to its damage output as possible, but Icicle Plate is a decent alternative if those items are already taken up on your team, or if you don't like the "side effects" from those items. I'm not sure if I would say it's "good," but that has more to do with Aurorus itself than the item choice.