Now that Serebii is now fully covering Sun & Moon stuff, it's time to show off the Sun & Moon edition of my used/unused type combination sheet:
Sun & Moon (including Alolan forms) introduced 13 new type combinations
There is
TECHNICALLY another type combination, but it's exclusive to Pokéstar Studios opponents in Black 2 & White 2
These guys (both named F-00) are both Steel/Normal type.
Gonna take a stab at what they could do with each type.
Normal-Ice: Lemming
Normal-Poison: Porcupine
Normal-Bug: Harvestman
Normal-Rock: Mountain Goat
Normal-Ghost: Opossum
Normal-Steel: Robot Dog
Fire-Grass: Tiki [HUGE MISSED OPPORTUNITY, GAMEFREAK]
Fire-Ice: Pokémon based on the concept of thermodynamics
Fire-Fairy: Victini retype, or like, a pyromaniac pixie
Electric-Fighting: Mega Electivire
Electric-Poison: Nuclear Reactor
Electric-Dark: Mega Luxray
Ice-Poison: Mega Avalugg, where it gains the ability to weaponize methane trapped within its iceberg.
Ice-Bug: an icy butterfly
Fighting-Ground: a Monk Pokémon based off an earthbender, or Mega Diggersby
Fighting-Fairy: Leprechaun please
Poison-Psychic: Brain
Poison-Steel: Ninja
Poison-Fairy: some little Sprite that has a venomous touch
Ground-Fairy: Starnosed Mole
Psychic-Bug: Earwig (based on the myth that they crawl inside your brain)
Bug-Dragon: Mega Flygon ;.;
Bug-Dark: Assassin Bug
Rock-Ghost: Gravestone
Dark-Fairy: Some devilish fairy that sneaks into homes and steals socks.