Hm...you have room for evil spirits, natural creatures, and mechanical monsters, not to mention elder abominations and C'thulhu...would it hurt to put in aliens as well? Provides an excellent source of Poison, Electric, and Ground types, all of which are a bit less numerous than the rest (plus more Psychics and Ghosts if you really want them).

So here are my suggestions for some alien 'mons:

- An pure electric-type, lightning ball Pokemon who exudes power to help allies. Slow, defensive creature with some Psychic-type moves to complement its Electric attacks and an ability similar to Cherrim's which buffs its allies during the rain.

- A ground/poison type burrowing alien monster, similar to the Zerg. Super-fast with Dig, evasion-lowering moves, multi-attacks, status...basically, cheap shots, if he had a third type it would be dark. A zergling->hydralisk->ultralisk evolution line could work with it.

- A steel/psychic, bug-eyed, ray-gun-toting alien invader (or maybe the guns are part of him?). In any case, moveset similar to Genesect or Octillery: LOTS OF BEAMS. Some of which should be unique. Steel/psychic is one of the best typing combinations in existence from what I know, so don't make this guy TOO powerful or he'll break the game...

- A pure bug-type, super-fast alien, similar to Ninjask but a special attacker. Uses either Compoundeyes or some kind of crit-buffing ability, like Sniper maybe. More of an annoyance than anything in-game, but like Ninjask it can Baton Pass (a good buffing move for it is probably Tail Glow)

- A pure dark-type mind-controlling alien, wimpy physically but carries every kind of manipulation move possible. Confuse Ray, Attract, Memento, Destiny Bond, Encore...you name it. Solid special defense, could be an enemy of the bug-type trying to exterminate it as a threat to his species.

At least one of these aliens should be placed similarly to Snorlax (probably the dark-type) in-game--the rest of them should be available just like any other 'mon.

What do you think?