Kinda going for a contrary elements. Fire/Ice is hot/cold, grass/ghost has a sort of life/death thing going, and water/flying has sea/sky.
On an entirely separate note, gamefaqs autocensor apparently hates this idea because I had to reorder the type list twice for it to not find a "censored" in between the lines.
Keep in mind how GameFreak always does the Grass beats Water beats Fire beats Grass thing. Even in the fourth gen, Empoleon may have picked up Steel, but Torterra got Ground, so it still had an advantage.
Water/Flying has no weakness to Grass, nor to Ghost. Quite the contrary, Grass/Ghost is weak to Flying.
Fighting type on the red starter contradicts this =)
I'd also like a Ghost/Rock type that changes forms depending on what stat is highest when it evolves (HP/Att/SpeA/Speed) with Levitate as it's ability
I also want a Poison/Steel and Poison/Rock type as well as a Grass/Fire type with Flash Fire as a regular ability and Storm Drain as a hidden ability (and sap sipper as it's secondary ability) that is a mixed attacker with a solid movepool.