Well max lvl is 10 so no wish spell (excluding scrolls, magic items etc which won't have it anyway).
Difficulty will be based upon levels as per DnD 5e.
I'm curious what the difference between 'Normal' difficulty , 'hard' and 'easy'. No. of enemies? Hp? Availability of health potions?
I would prefer higher difficulty changes AI, enemy skills etc so each combat is both harder and different. Increases replayability. And difficulty is Optional so more casual players are not put off.
If they have access to WoTC resources and it´s based in 5e, increasing the difficulty is as easy as increase (or decrease) the CR level of the encounters. There are tables that allow you to do that in DM and campaign resource materials. To increase the level of the encounter those tables usually increase the enemies´ stats, numbers, add new abilities or equipment, depending on the creatures.
