Mists of Salamira
Classes with spell preparation
Clerics, Druids and Wizards are altered in game mechanics but the concept and their place in the world remain the same. These classes have to spend at least their level in days each month to maintain their connection with the source of their power. In return, they have the ability to use higher level spells their classes would normally allow in exchange for some temporary hit points.
Clerics use this time to make sure their connection to their god and church/sect is still strong and pure by performing masses and in silent prayer. Druids return to the circles in glades and marshes that had trained them and spend this time in isolation as close to nature as possible. Wizards study ancient inscriptions and perform rites among themselves in the covenant or tower.
If completing this duty, the three classes are able to perform spells at most 2 levels higher than they originally could. The cost of higher level spells is calculated as such: (cast spell level – highest available spell level) x cast spell level + cast spell level.
Spells that are to be cast in this manner also need to have a (lower level) slot prepared for them and a third of the hp is lost in preparation. This temporary hp cannot be recovered until the character uses her higher level spell or completes a long rest.
Casting a level 5 spell for someone that is supposed to cast only level 3 would be (5-3)x5+5= 15 hp, 5 of which would be spent to create a temporary slot for the spell when preparing.