Shadow Alolan Marowak

Alolan Marowak doesn't have any of the distinguishing features that it has in the main Pokemon games. No Thick Club, no Lightningrod. I guess it kind of got boned in that respect. Even Shadow Bone is less powerful than Shadow Ball in PvE. Poor stats doesn't help much either. 

Best PvE Offensive Moveset

• Fire Spin performs the best, but only pairs with Fire Blast to fulfill a Fire-type role. 
• Hex isn't far behind, and pairs with Alolan Marowak's stronger Ghost-type charge moves.
• Rock Smash lacks STAB and isn't recommended. 
• Shadow Ball is superior to Shadow Bone* on offense. 
• Flame Wheel is a pretty poor move, despite benefiting from STAB. 
• Bone Club has no use. 

Best PvE Defensive Moveset

• Rock Smash is likely to perform the best on defense, being Super Effective vs Dark-type attackers.
• Fire Spin sports higher base damage than Hex, though the latter generates energy faster. 
• Bone Club doesn't threaten a lot of damage, but can be used frequently as a 3-bar move, and hurts Rock-type attackers.
• Flame Wheel is the weakest among the available 2-bar moves, but is slightly harder to dodge. 
• Shadow Ball is superior to Shadow Bone* in terms of damage, with very minor differences in damage windows. 

Fire Spin is generally Alolan Marowak's best option due to its overall above average parameters; it also grants Alolan Marowak a reliable source of Fire-type damage. Hex has higher energy gains, but suffers from having a MUCH lower damage output. Rock Smash is bad.

Bone Club costs the least amount of energy and provides coverage against certain Rock-, Electric-, and Poison-type Pokemon. Shadow Bone* is an excellent Ghost STAB move that dents anything that doesn't resist it; it also has a decent Defense debuff chance. Shadow Ball is a decent non-Elite alternative; it has greater DPE, but its higher cost makes it a less consistent option. Fire Blast can surprise unsuspecting Normal- and Dark-type Pokemon who otherwise can take Alolan Marowak's Charged Attacks with ease, but don't expect any kind of consistent performance due to its insane cost. Flame Wheel is horrendous.