I have never liked the idea of having only a few spells "prepared" each day. So we're going to do away with that entirely.
Casters can cast any spell in their spellbook and that use takes up a "spell slot" for the day. This means that you can cast "Hide from Undead" or "Cure Light Wounds" without having to prepare either one.
Casters are still required to Rest/Commune with their god/Chill with nature/Etc. the time required to normally memorize their spells before they regain their spell slots. (Excepting sorcerers, they just need a normal sleep period.)
Sorcerers also gain the benefit of changing out any known spell for another spell after a number of dedicated days of research equal to the spell level of the spell they wish to learn. (Half a day for cantrips)
Note these rules apply to PCs and NPCs equally.
Exception - Repeated Casting
Repeatedly casting the same spell has drawbacks. Spells may only be cast twice per day without sleep or a long rest without side effects. (Note, this does not apply to sorcerers or other "spell limited" casters.)
- A third casting of the same spell in a day has a 50% chance of a side effect.
- A fourth casting has a 75% chance of a side effect.
- Casting a spell a fifth time or more has a 100% (certain) chance of triggering a side effect.
When a side effect is triggered the original spell has a 50% chance of failing outright (the spell slot that was being used is consumed if the spell fails), and a roll is made on the following table regardless of whether the spell failed or not.
d% Side Effect
01-15 The caster takes 1d6 points of damage per spell level.
16-20 The caster is affected by a slow spell for 5 rounds.
21-25 The spell takes effect at a random location within the spell’s range.
26-30 The caster is confused for 3 rounds (as confusion).
31-35 The caster is dazed for 3 rounds (as daze monster).
36-40 The caster falls asleep for 1 minute (as sleep).
41-45 The caster can’t cast or concentrate on spells for 3 rounds.
46-50 The caster is affected by reduce person for 1 minute.
51-55 The caster becomes sickened for 5 rounds.
56-60 A zone of truth appears, centered on the caster.
61-65 The caster is affected as if targeted by the spell.
66-70 The spell’s area or the targets of the spell become affected by silence for 3 rounds.
71-75 The area of the spell is filled with daylight.
76-80 The spell’s area of effect is coated in grease.
81-85 A random creature from the summon monster I list is summoned in a square adjacent to the caster. It is not under the caster’s control.
86-90 The caster is affected by tongues for 10 minutes.
90-94 An additional spell slot is consumed randomly from the caster's remaining unused slots.
94-95 Roll twice on this table.
96-97 Roll three times on this table.
98-99 Roll four times on this table.
100 Roll five times on this table.
Also a side effect might occur that you are completely unaware of at the time.
A ritual (explained below) may be cast more than 2 times without drawback. So a character can cast "Divination" twice normally and then once as a Ritual without side effect. However, three "normal" castings would cause a side effect.
Exception - Rituals
The following list of spells can be cast without using a spell slot as "rituals".
- Animal Messenger
- Commune with Nature
- Comprehend Languages
- Contact Other Plane
- Instant Summons
- Gentle Repose
- Illusory Script
- Tiny Hut
- Magic Mouth
- Meld into Stone
- Phantom Steed
- Telepathic Bond
- Speak with Animals
- Floating Disk
- Unseen Servant
- Water Breathing
- Water Walk
Rituals take 10 minutes longer to cast than normal. Because it does not expend a spell slot a ritual cannot be cast at a higher level.