Shadow Aurorus

Shadow Aurorus doesn't gain a whole lot in terms of raid viability. It's obviously better than its base forme, and it CAN pull double-duty with really good movesets for both Rock and Ice, so it's okay when just starting out, but even then it's way too expensive to be worth the investment.

• Frost Breath tends to edge out Powder Snow on offense, but the two are very similar.
• Rock Throw pairs with Meteor Beam for Rock-type offense.
• Weather Ball Ice is the best Charge Move for Ice-type offense, and is consistent as a 3-bar move.
• Blizzard is a direct downgrade. 
• Ancient Power is lackluster.
• Thunderbolt should be used by Electric-type Pokemon.
• Hyper Beam can't benefit from a Super Effective multiplier. 

Best PvE Defensive Moveset

• Frost Breath is less likely to be resisted on defense, making it more favorable than other available options.
• Rock Throw will be resisted by common Fighting-type attackers, but is otherwise decent with STAB.
• Powder Snow has poor damage output on defense. 
• Weather Ball Ice can be spammed frequently on defense, making it the best option for damaging attackers. 
• Ancient Power may be a 3-bar move, but its slow animation is very easy to dodge, and is also resisted by ubiquitous Fighting-type attackers.
• Meteor Beam is strong, but Shadow Aurorus is unlikely to get to it on defense due to the prevalence of Fighting and Steel Types
• Thunderbolt is good against Water Pokemon that would seek to prey on Shadow Aurorus.
• Blizzard hits hard and fast, but Shadow Aurorus might faint before it can use it. 
• Hyper Beam sucks for defense. 

Powder Snow is generally recommended for its high energy generation, letting Aurorus spam its Charge Moves often. Rock Throw or Frost Breath are alternative choices that deal strong STAB damage, but are lackluster on energy gains.

Aurorus gets access to the Ice-type variant of Weather Ball, which is cheap on energy and can be spammed frequently. Thunderbolt is recommended for its moderate energy demands compared to other available Charge Moves, and can be useful against common Water Pokemon. Ancient Power is a very inefficient Charge Move despite benefiting from STAB, and does not deal enough damage for its energy cost to be viable. Hyper Beam demands too much energy, while Blizzard is redundant and less consistent than Weather Ball.