jellicent is a unique water type because of its ghost typing, which gives it access to tools such as will o wisp, immunities to normal/fighting, and taunt. it has access to reliable recovery, enough special bulk to invest fully in its physical bulk, and enough speed to outspeed other walls. it also has enough of a wally reputation to maybe pull off a surprise offensive set (scarf water spout anyone?). however, that ghost typing that gives it uniqueness is also a curse, because its heaivy susceptible to knock off, which it does not appreciate. it can be worn down by toxic, entry hazards, and can't always switch in repeatedly.
Number 18: Jellicent