Ghostly possession doesn't need to be a bad thing in Dungeons & Dragons. One of the core abilities of ghosts in Dungeons & Dragons is the ability to possess humanoids, which usually results in friends becoming foes during combat. Dealing with a party member possessed by a ghost is tough, but it's a problem easily solved by the dispel good or evil or a cleric's Turn Undead ability. However, not every ghost is necessarily malevolent and a "willing possession" can introduce some fun opportunities for both roleplay and some interesting game mechanics.
In my home game, the party's cleric Averil cleansed the spirit of an ancient warrior who had ties to a fabled order of knights. But while the ghost had the opportunity to "move on" to the next plane of existence, she chose to occupy Averil's body as she sensed that the evil that led to her demise was returning to the world. From a mechanical perspective, choosing to let the ghost occupy her body resulted in a proficiency on History checks involving the ancient past and a cool ghostly scythe that she could summon at will.
Eventually, sharing a body with a ghost did have its consequences for Averil. Recently, I made Averil's player make a Wisdom saving throw at the start of her day. When Averil failed the saving throw, the player was secretly presented with some new guidelines - instead of controlling Averil, she was now playing as the ghost possessing Averil's body....complete with an entirely new character sheet. Instead of a Grave Domain cleric, the player now was temporarily playing as a paladin, complete with the paladin's divine smite ability and the ability to lay on hands to heal players. And instead of roleplaying as a sullen teen, the player got to play as and learn about the strong and powerful warrior she had adopted... albeit with a couple of drawbacks. After all, the ghost doesn't have any fellowship with Averil's party, and Averil is a relatively squishy cleric who isn't necessarily made for the front-line combat and direct approach that the ghost craves.
It didn't take too long for the rest of the party to figure out what was happening to their cleric, but it did make for a great mini-mystery that added to the roleplaying and social parts of our D&D session. Plus, giving a player two different character sheets and making them roll to determine which one they used during a given day seemed like a fun way to add both a boon and a bane for a player. With some collaboration between the DM and player, ghostly possession doesn't need to be limited to combat or haunted house exploration. Instead you could make a hidden soul occupying a body a core part of a character's background - a way to add some mystery and intrigue to any campaign.
How do you handle friendly D&D spirits at your table? Let us know in the comment section or find me on Twitter at @CHofferCBus to chat all things D&D!