You need to attach a dragon scale and trade it
It doesn't evolve at a certain level, it evolves into Kingdra when traded holding a Dragon Scale.
Give it a Dragon Scale and trade.
make it hold the item "dragon scale" and then trade it
Level 18.
Level 30.
Level 30.
level 28
Level 25
Level 37.
Level 26
at level 40 it should evolve into drapion
Spiritomb doesn't evolve.