There are a few key points associated with gaining XP and leveling up that I wanted to go over.
Fighting or otherwise defeating monsters will return immediate XP, so if the party is stuck in the wilderness, they can still level up. Discovered copper, silver, electrum, gold, or platinum gives XP as soon as civilization is reached; any town, keep, or sufficiently large camp counts. Non-magical treasure becomes XP the moment it's sold (or, if sold outside of civilization, as soon as civilization is reached). Magical treasure is a bit different; if ever used in any way, it may not be converted to XP when sold. If unused, then whatever price it sells for will become XP, as normal treasure. Note, however, that "used" includes hiring a sage or sparring with a weapon or armor to discover its properties; selling magical items for XP, therefore, comes with no little risk, as you have no idea if you are getting ripped off or not. Was that magical sword you sold for 5000 gp actually just a basic Sword +1, or was it a Luck Sword with three wishes? You're more likely to get a better offer from a shopkeeper in a bigger market.
For the most part, characters will level up as soon as they hit a city and redeem their XP, or sooner if they got enough XP from fighting monsters. New general and class proficiencies can be applied at any time apart from combat - that is, immediately, or held until a need arises, which means a familiar could suddenly appear, or a character could suddenly remember she knows how to track. Clerics and other prayerful spellcasters gain immediate access to any new spells, as do spellcasters with inherited spells. Mages, Warlocks, and other such studious magic users, however, must find new spells. There are three ways for a mage to add new spells to his repertoire:
- Studying for a week at a mage college; this will teach any number of spells, up to the total the mage can cast in a day. Adding an additional 1st level spell takes a week; added a brand-new level 2 spell, as well as 2 from high Int, will take 3 weeks.
- Finding a scroll or spellbook the caster can read; the mage can copy the spell into his own spellbook for free, though it takes a week. Scrolls are used up, but not spellbooks.
- Researching a spell (new or not); this takes money and time - a library worth 4,000 gp, plus 2,000 gp per spell level researched, an additional 1,000 gp per spell level cost, and 2 weeks per spell level.
I realize this puts even more hardships on mages; so, I have decided to add a house rule: mages, and any similar classes, may use crossbows. This includes mages, warlocks, and librarians. However, they can only fire every-other round; between firing, they must re-wind their crossbow, which takes longer since they are not as skilled as others.