Shadow Drapion

Drapion is more of a well-rounded Pokemon; with no highlights of extraordinary stats or epic movesets, Drapion kind of falls in the middle of the pack in Great League. It isn't the only Pokemon with the interesting Dark/Poison typing, which means it has a lot of competition to fulfill its role. What makes Drapion sort of stand out is its larger moveset diversity, which enables it to be more versatile. Among the Dark-types and Poison-types in this league, Drapion's numerous moveset options gives it a lot of flexibility, with options for frequent charge move spam or fast move damage pressure. Unfortunately it's not quite at the level of top tier meta Pokemon, so Drapion tends to see more use in specific formats that cater to its strengths. 

Shadow Drapion tends to be preferable to regular Drapion. This is because Drapion's lightning-fast Charged Attacks outpace most Pokemon in the game. The overall reliability of Shadow Drapion's damage allows it to make excellent use of the Shadow Bonus and makes up for the bulk penalty of being a Shadow Pokemon.

The level 50 update increases Drapion's performance in Ultra League, allowing it to reach the 2500 CP cap while increasing its IV optimization for more bulk stats. Dark typing at first glance might seem appealing against the popular Giratina, but Drapion can struggle against Dragon Breath variants even with both Bite and Crunch. Access to Aqua Tail is a great option to deal unresisted damage to other Dark/Poison Pokemon like Skuntank or Alolan Muk, giving Drapion an advantage. Unfortunately Aqua Tail is generally considered a weaker move in the meta, and without STAB Drapion tends to struggle against more neutral matchups. 

Drapion doesn't have sufficient stats to perform well in Master League. Most of the wins it will get would be against off-meta picks weak to its typing, which isn't saying much.