Season 18: The Ghost Doom

Main villain's Morro while the ghosts are the villains

Episodes
205. Doom of the Destruction Master

206. Revenge

207. Oceanjitzu

208. Attack from Ghosts

209. The never-Ever-Ever Ending

210. Ghosts and Darkness

211. The Allied Armor

212. The Ghost Ninja

211. The Yellow Ninja

212. No Such thing that's an Yellow Ninja

213. Reign of the Brown Ninja

214. IS it The End?

Protagonist
Wu.