Shadow Abomasnow

Shadow Abomasnow skirts being a great Pokemon, usually sitting just outside of the truly optimal counters save the rare cases where its awkward type-combo actually comes in handy for one reason or another. That said, this is a Pokemon capable of putting in work from the Grass and Ice sides of the spectrum alike, so it's a solid investment for any new players who happen to score a high-IV Shadow Snorver.

Best PvE Offensive Moveset

• Leafage is the better fast move on offense, and hits hard with STAB.
• Powder Snow takes better advantage of Shadow Abomasnow's stronger Ice-type charge moves. 
• Weather Ball (Ice) is the best charge move available, and helps to fulfill an Ice-type role.
• Blizzard and Icy Wind are a step down. 
• Energy Ball isn't particularly strong, but can enable Shadow Abomasnow to be a good Grass-type attacker. 
• Outrage has no use, and Razor Leaf is sub-par.

Best PvE Defensive Moveset

• Razor Leaf sports more than double the base power of Powder Snow or Leafage, making it better on defense. 
• Weather Ball (Ice) is the best charge move for defense, can be used frequently as a 3-bar move, and is harder to dodge. 
• Icy Wind is slightly stronger than Weather Ball, but only a small amount, and as a trade-off it's also easier to dodge.
• Outrage offers relatively neutral coverage as a 2-bar move, but is easier to dodge. 
• Energy Ball benefits from STAB but is very slow and predictable. 
• Blizzard is a 1-bar move, which means this snow man might melt to Fire-type attacks before being able to use it. 

The rebalance to Abomasnow following the July 2020 introduction of Season 3 in Go Battle League gave the snowman much needed tools to its moveset. Powder Snow is now recommended for its fast energy generation. Razor Leaf features incredible damage output with STAB, but is held back by the worst energy gains in PvP. Leafage is a decent move, having relatively balanced damage and energy, and can be a viable choice, but Abomasnow often prefers to focus on its Ice-type damage due to it being a superior offensive type.

The addition of Weather Ball (Ice) is a significant improvement, costing low amounts of energy for very respectable DPE (Damage Per Energy) efficiency, and can be spammed very frequently. However, Icy Wind can be used instead, sacrificing pacing for additional utility. Energy Ball is recommended with Powder Snow movesets for additional STAB coverage. Outrage costs a lot of energy and is generally not recommended, but can be useful with Razor Leaf movesets. 

Generally speaking, regular Abomasnow prefers Icy Wind as it can stick around to debuff its opponents a few times, while the more fragile Shadow Abomasnow prefers Weather Ball Ice.