It would be a dragon type Or rock type
I would go for a water rock type like corsola
Water/rock types are resistant to
Rock
Normal
Poison
Fire
Ice
Neutral damage from 7types
Maybe a poison bug resists
Poison
Bug
Grass
Fighting
Neutral damage from 8 types
Or even a dragon type
Resists ...
Fire
Grass
Water
Electric
Neutral damage from 11 types
Chart here
Of course there's magnezone which you didn't want Steel types but 12resistances and 1 immunity 2with magnet rise or air balloon
Finally you could kind of count shedinja
12immunitys 2resisyances that's considering it has wonder guard