I might be flamed for this but it would be interesting if they did a 'Virus', 'Zombie', 'Host', 'Cure' 'Immune' Pokemon cycle type thing.
I really don't know how to explain it but here I go
Host Pokemon are just regular typed Pokemon And can evolve into either Zombie Pokemon by being bit/infected by a Virus Pokemon (Poison?), which only can produced by Zombie Pokemon (Poison/Ghost(Undead)). Or stinged by a Cure Pokemon(Type Unknown) to evolve into a Immune Pokemon (Type Unknown). And The Host Pokemon is the only one that can be infected, no other Pokemon.
The Cure and Virus Pokemon must need a Host Pokemon to evolve into their final Evolution.
I was think a way to get infected by the virus or cure, is by in battle with a WILD Virus or Cure Pokemon. If the Virus Pokemon uses Bite or Cure Pokemon uses sting on the Host. It injects what ever into the Host Pokemon. And after the battle the Host will evolve into the respected Pokemon and the Cure or Virus Pokemon disappears to evolve with the Host Pokemon. Or some sort of way.
Zombies/Virus Pokemon have a speed, defense, attack Bonus during the night, and the reverse deduction in the day. Virus more common appeared at at night Uncommon for Zommbie, But Both rarely appear during the day, in the wild. While Immune/Cure Pokemon have Speed, defense, attack bonus during the day, and vise versa. Wild also goes for the Immune and Cure Pokemon but opposite.
I know it sounds complicated but easy to understand once get it.
Don't kill me for my idea...