Note that I have a female Mii for my save file, so....
Princess's Robe (Princessa's dress): Place first in Castle Trodain, standard rules. Waluigi's Wear: Place first in Delfino Plaza, standard rules. Boo: Place second or first in Starship Mario, standard rules.
I'm not sure about these below. Peach's Dress?: Place first in Peach's Castle, standard rules. She-slime: Second or higher on Slimenia easy rules? Man o' War: First on either the Observatory or Ghost Ship easy rules. Devil's Tail: I think I got after Mt. Magmageddon easy rules. Chain Chomp: Win the third Special Tour map on easy rules? Fortune Street Ranger Uniform: I got it after placing first in the second Special Tour map on easy rules, but I don't know if you get it beforehand.
Luma might be unlocked on the fourth board of the Special Tour or Starship Mario first place on standard rules. I know you don't get it on easy rules.