One could easily assume Noctowl to be part-Psychic. Same goes for Stantler, to a lesser extent.
Gligar could just as well be part-Poison, or even Bug.
I can never remember whether Steelix is Steel/Ground or Steel/Rock.
I vaguely remember thinking Hitmontop was Fighting/Ground the first time I saw it.
Nobody would ever have gussed Azurill was Normal.
Illumise and Volbeat could easily be mistaken for Bug/Flying, given their wings and tendency to fly.
Much like Gligar, Flygon could pass for any combination of Ground, Dragon, Bug, and Flying.
I thought Altaria was plain old Normal/Flying like its pre-evolution.
Anorith and Armaldo just scream, 'Water'.
I sort of expected Chimecho to be Normal or perhaps Ghost.
Don't lie -- You and I both thought Empoleon was Water/Ice.
Since when is metal, like that which one variety of Wormadam is coated in, pink?
I expected Glameow and Purugly to be what Purrloin and Liepard are.
It was pretty gay to make Lucario's second type Steel rather than Psychic or something.
Being based partially on a shark, one might think Garchomp's line is part-Water.
I really and truly thought Roggenrola and its evolutions would be Rock/Ground.
Cottonee and Whimsicott struck me as Grass/Flying, much like Hoppip and co.
Darmanitan looks like abandoned concept art for another Fire/Fighting starter.
I thought Solosis, Duosion and Reuniclus would be Poison, being base don microorganisms and all.
Shelmet really should be Bug/Steel like Escavalier. They're both covered in armour.
Alomomola struck me as Psychic, or Water/Psy.
Beheeyem's earthen colours give it a part-Ground look.
Stunfisk was originally intended to be a Water-type, and it still looks like one.
If Braviary, the very embodiment of America, isn't Fighting-type, who really is?
Heatmor's pipes and mufflers make it look like more of a Steel-type than Heatran.
I never would have guessed the Musketeers were half-Fighting.
