An arcane spellcaster has the ability to independently research new spells, duplicating an existing spell or potentially creating an entirely new one. If characters are allowed to develop new spells, use these guidelines to handle the situation.
Any kind of spellcaster can create a new spell. The research involved requires access to a retreat conducive to uninterrupted meditation, study, and focus. Research involves an expenditure of 200 XP per week and takes one week per level of the spell being researched. At the end of that time, the character makes an Arcane Lore check (DC 10 + spell level).
If that check succeeds, the character learns the new spell if her research produced a viable spell. She has the spell prepared and ready to be cast, but if she wants to record it for later use, she will need to record it in her spellbook or onto a scroll (paying the normal costs). If she is a spontaneous spellcaster, the spell is added to her list of spells known, but she is unable to actually cast the new spell until she regains her spell slots after a long rest.
If the Arcane Lore check fails, the character loses any expended XP must begin the research process again if she wants to keep trying.
Limitations of Research
Researching and learning new spells in this way is exceptionally difficult.
Prepared Spellcasters
A prepared spellcaster who uses a spellbook can learn any number of spells this way, but she must pay the research costs in addition to the normal costs for writing a spell in her spellbook. After successfully researching a spell, the spellcaster must pay the normal costs to record the spell in her spellbook before she can prepare and use the spell. If she begins research on any new spells before recording the spell, she forgets that spell and must research it again.
A spellcaster who prepares spells but does not use a spellbook—such as by having access to all spells on their spell list, being limited by spells known, or some other system—is treated as a spontaneous spellcaster for determining the maximum number of spells she can research (see below).
Spontaneous Spellcasters
A spontaneous spellcaster with a limited list of spells known can learn a maximum number of spells through research whose total combined spell level is less than or equal to half her Intelligence score, rounded down. For example, if she has an Intelligence score of 16, she can learn up to 8 levels worth of spells. This could be three 1st-level spells, two 2nd-level spells, and a 3rd-level spell or one 7th-level and one 1st-level spell or any other combination that adds up to 8 or less.
If she researches spells for more than one spontaneous spellcasting class, she adds together the total level of researched spells for all of her classes to determine if she has reached her maximum number of researched spells.
Research Beyond the Limit
A spontaneous spellcaster may choose to research a spell that would put her beyond her maximum number of researched spells; however, she must immediately forget a number of spells she has researched (including the one she just finished researching, if so desired) until the combined spell level of her researched spells is below her maximum number.
Though she loses access to the spell, she retains some memory of the lost spell. If a spellcaster permanently forgets a researched spell, she may research it again at half the normal cost. She may also research a spell she has forgotten through the normal level up process (if her class permits doing that) for half the normal cost, as she still retains some memory of the spell.
Ability Damage and Drain
Reductions in a spontaneous spellcaster’s Intelligence score (such are through penalties or ability damage) do not cause her to lose any spells she has already researched but may prevent her from researching new spells if the temporarily lowered score would reduce her maximum number of researched spells. Likewise, temporary increases to Intelligence such as from spells or magic items does not increase the maximum number of spells she can research.