We just played our weekly game and one of our PCs cast dispel magic and we got confused with the wording of the DC to dispel. Is the rise in DC based on the spell slot level used or the normal level of the spell?
The DC to dispel a spell effect is based on the spell's slot level.
Dispel magic says:
Any spell of 3rd level or lower on the target ends. For each spell of 4th level or higher on the target, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level.
The rules for spell slots say:
When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell assumes the higher level for that casting. For instance, if Umara casts magic missile using one of her 2nd-level slots, that magic missile is 2nd level. Effectively, the spell expands to fill the slot it is put into.
So a spell that is normally 1st level cast with a 4th level slot is a 4th level spell. Therefore the DC to dispel it would be 10 + 4 = 14. A spell's level is determined by the level of the slot used to cast it.