Ok once per game day you can get a new costume only after I got the costume cancelled and traded did I recieve items.
First day traded cookie got yagudo costume. Cancelled it and traded more of the same sweets to different npc's got Trick Staff II.
Waited a day traded got costume cancelled and trade about three more sweets to different NPC;s and got pumpkin head.
Last day traded got quadav costume cancelled and traded 3 or 4 more cookies to random NPC's got pumpkin head II.
To my knowledge any sweet works as well as the other.
Will update as the days prgress hope this helps.