A list of unused type combinations (as of usum)

Normal/Ice
Normal/Poison
Normal/Rock
Normal/Steel
Normal/Ghost
Fire/Grass
Fire/Ice
Fire/Fairy
Electric/Fighting
Electric/Poison
Electric/Dark
Ice/Poison
Ice/Bug
Fighting/Ground
Fighting/Fairy
Poison/Psychic
Poison/Steel
Poison/Fairy
Ground/Fairy
Psychic/Bug
Bug/Dragon
Bug/Dark
Rock/Ghost
Dark/Fairy