How do you get Spiritomb in Pokémon Diamond and Pearl?

Spiritomb, the ghost of 108 spirits bound into a stone, is never found in the wild in Sinnoh. To summon one you first need an Odd Keystone: a man on Route 208 hands one over, another hides in Twinleaf Town, and more can be dug out of the Underground walls. Take the stone to Route 209 and set it into the crumbling ruin there, which becomes the Hallowed Tower.

Then comes the part that made Spiritomb famous. The tower wakes only after you have greeted other players 32 times down in the Underground. These had to be real people on real DS systems nearby, since the Sinnoh Underground ran on local wireless; the hiker NPCs who live below do not count. The tower's inscription changes as you progress, from silence, to crying, to shaking, to a presence ready to emerge.

There is a mercy built into the rule. The 32 greetings do not need 32 different people. If one of you steps out of the Underground, or slips in and out of a Secret Base door, between greetings, the same friend counts again, so two determined players with two DS systems can grind out all 32 together. Check the tower at 32 and a level 25 Spiritomb attacks at once.

The ritual can be repeated with a fresh keystone for another Spiritomb. Because the Underground is local wireless rather than a server feature, the whole ceremony still works today, untouched by the 2014 shutdown, as long as two cartridges and two systems are in the same room.