you can get items from events such as a christmas event so I was wondering. is there a higher chance of an actually good item on a higher difficulty? and if so does it have to be found on that difficulty?
schthack had an event where you would get some presents in any difficulty, area or enemy, but depending on the difficulty you find it the different the prize.
It's obvious that in ultimate you get the best items but there were also chances of getting common items like monomates or materials.
That event is gone i believe, so your best solution is to wait for other events.
Seasonal events don't alter drop rates, but they replace the normal love rappy (temple) with the specific seasonal rappy and that rappy gives you either a present, a jack-o-lantern or an easter egg (depending on the seasonal event)
^that post sums everything up. ^.^