Mega Aurorus' signature weather-setting ability Diamond Dust has
3 major implications, which I'll explore in as much detail as possible:
1) Immunity to all Rock-type attacks- On the surface, this is easy to mistake for a simple immunity. Rock is one of Aurorus' weaknesses, and its ability nullifies this. But Stone Edge is often famously coupled with Earthquake, which it is also weak to. This is where Aurorus' teammates come into the picture. By pairing it with a Flying-type, you can gain complete immunity to
EdgeQuake, one of the most powerful move combinations in the game. Not only does this stop devastating threats like
Garchomp and
Lando-T, but it also lets your Flying-type Defog more easily. Speaking of which,
2) Immunity to Stealth Rock- Due to the unfortunate way in which weather-setting abilities work, it is difficult for Mega Aurorus itself to benefit from this, as it takes hazard damage
before setting Diamond Dust. Once again, the effect is mostly designed for use by its allies. Defog is a move mainly learned by Flying-types, and they will often run
Heavy-Duty Boots to avoid Stealth Rock damage. However, a well-timed Knock Off can remove Boots, which doesn't do much outside of stopping Rocks. Diamond Dust solves all of this, letting you not fear Knock on your HDB
and even run different items like
Leftovers or
Rocky Helmet. But that's not all. More offensive Pokemon, like
Volcarona and
Weavile, can run items like Psychium Z or Choice Band more comfortably, becoming much more threatening.
3) Acting as Hail- While Diamond Dust lacks the chip damage of Hail, all weather related moves and abilities function as they do in Hail. This means Aurorus can set up Aurora Veil and Volt Switch into a Slush Rush teammate.
Arctozolt can be especially strong with STAB pesudo-BoltBeam, whereas
Arctovish hits like a truck with Fishous Rend. These two are also weak to Stealth Rock, which is why Diamond Dust works so well for them. In addition to this, Weather Ball can be run as Ice-type coverage on various other Pokemon.
As you can probably tell by now, Aurorus' role is mostly supportive. I've played it using Veil, Volt Switch, BoltBlizzard, paired with various different Stealth Rock-weak and Hail-based mons. With that being said, I believe
Mega Garbodor currently outclasses this, with complete hazard removal that even powers up its own Body Press. There is also a Calm Mind set that can be very overwhelming in the right circumstances, but
Mega Walrein and
Mega Vanilluxe are more reliably strong Ice types. Currently, Aurorus is only really good in VGC, due to the supportive properties discussed earlier being much more prominent in a Doubles format. Now you might ask, how does that change in Kalos?