Since Halloween, the special study "A scary message" has been published. This is one of the shortest tasks in terms of the numb...
As far as Mew is concerned, the special study is divided into several special missions that have to be carried out in order. However, the quests contained in these missions can be fulfilled without following a specific order. Spiritomb is far from the only reward you will receive in this study because you will receive a reward for every mission or quest you have completed.
Here are the contents of the 3 special missions that must be completed sequentially:

Mission 1
- Catches 10 spectrum type Pokémon- made 8 big throws
- Use 108 berries to catch Pokemon
Mission 2
- Catches 10 dark Pokémon- Make 8 Pokéstops you've never seen before
- Catches 108 Pokémon
When you catch the 108 creatures, Spiritomb appears! You can capture it even if you have not completed the other two quests in step 2 yet.
Mission 3
- Capture Spiritomb- Capture Spiritomb
- Capture Spiritomb
You will probably have noticed that Mission 3 will automatically be validated if you do not miss Mission 2. Even if the presence of this third mission can be called into question, we will not spit on the experience and the many sweets given to us after completing all the special studies.