For Founders’ Fortune players, this event can be triggered in all game modes and a ghost can join your village at any time, even if your villagers are not completely satisfied, angry and whatnot. This is what you need to do for the achievement
Save the game before the summoning
Before triggering the ghost after gathering the resources needed for the summoning, it is important to save the game(!) you might summon a red ghost, which will attack the village – you can only defeat this ghost and gain a permanent mood boost, but this is not what this this guide is about. Simply reload before summoning the ghost, until a blue ghost enters the village to seek closure.
Use Diplomacy
It is important to make the summoner (the character who triggered the ghost event) immediately talk with the ghost to befriend it. Apologize to the ghost before the day ends and gain its friendship. Ideally – the summoner is in possession of the diplomacy skill. Each time you would give the ghost a hug, you will see that “diplomatic relations” will improve. You can try to use another character with a diplomat skill to talk with the ghost before the 1st day of summoning ends – but using the summoner worked for me.
Say goodbye with a hug
Have the summoner say goodbye to the ghost, by hugging it.
This will make the ghost remain in your village.
Pls comment in the section below if you have troubles, thumbs up if this worked for you as well.