Aurorus

Aurorus is a very vulnerable Ice/Rock Pokemon, despite boasting a respectable STA stat. Its disastrous typing does it no favors for gym defense, being doubly weak to ubiquitous Fighting-type attackers, as well as weaknesses to multiple other common typings. Its ATK stat isn't very high either, resulting in subpar performance for attacking raids and gyms. 

Best PvE Offensive Moveset

• 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 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 Aurorus.
• Blizzard hits hard and fast, but 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.