Doing a countdown based entirely on a single series can be a double-edged Aegislash. It makes the roster easy to plan out and allows you to pay homage to something that you have a strong connection to, but it also takes a lot of the guess work out of it and can potentially get stale for the audience unless you're able to be pretty creative with it! These are probably best left to smaller countdowns which unfortunately I didn't do but you know what they say; the best laid plans of Rattata and men!
Looking back on it, it's easy to view the unidentified "GHOST" sprite as sort of a non-entry, but I couldn't very well do an entire Pokemon themed Halloween Countdown without it! Like I said, you got to be creative! What fun would it be if I just reserved the the top two spots for my favorite or canonically 'strongest' Ghost or Dark Pokemon? You gotta keep people on their toes and, in the case of Halloween, on pins and needles. The sheer levels of terror this and Lavender Town in general created in people of my generation is nothing short of impressive for an 8-bit game about magical animals and thanks to the volume of Creepypastas surrounding it, it shall live on in our childhood trauma forever more!