To acquire Spiritomb in the Crown Tundra, you’ll need to first find a gravestone that contains a riddle then solve it. To locate this gravestone, travel to Dyna Tree Hill in the Crown Tundra. With your back to the giant tree, take a right when the path forks. Follow this path a short distance to travel past a berry tree on the right side. When you reach this berry tree, hug the left side of the road. Go past a patch of tall grass and head towards the tree. After the tree, follow the path down then take a left. Hug the right side of the cliff to reach a tombstone underneath a tree at the dead end.
Once you reach the tombstone, interact with it to acquire the following riddle: “Spread my voice.” To solve this riddle, you’ll need to be online. After you have connected to the internet, you will then need to interact with 60 different actual people playing the game in the Wild Area. While talking to these individuals, you’ll receive items from them and can go back and interact with the tombstone to check on your status. When you interact with 30 people, the tombstone will say “You can sense a presence within… It feels like something could pop out at any time!” After interacting with 35, the tombstone will read “My voice has been heard.”
Unfortunately, Spiritomb did not show up for us at the gravestone until after we spoke with 60 different individuals. Once we spoke to all these people, Spiritomb appeared in front of the tombstone. Save the game if you wish to shiny hunt it. When ready, interact with it for the chance to catch it!