The edit is that it would learn it naturally. And I forgot about abilities LOL. So yeah, Water/Dragon.
Also, what about this for Morty:
Misdreavus/Gastly/Haunter/Haunter/Haunter/Gengar (sets coming SOONTM)
Misdreavus: Pain Split/Curse/Double Team/Confuse Ray (EVs on the defenses)
Gastly: Perish Song/Destinny Bond/Mean Look/Spite (Max Speed), with a new BST of 340 (30/35/30/100/35/110) (crazy in that it outspeeds Haunter, but it could be because it's smaller :^])
Haunter nº1: Hypnosis/Dream Eater/Shadow Ball/Nightmare (Max Speed)
Haunter nº2: Thief/Psychic/Thunderbolt/Giga Drain (Max SpAtk and Speed)
Haunter nº3: Night Shade/Hypnosis/Nightmare/Confuse Ray (higher leveled that everything else but Gengar)
Gengar (ACE): Night Shade/Giga Drain/Fire Punch/Ice Punch (Max SpAtk and Speed)
medium-ish levels to make it a little bit less OP