Is everybody sick of reading about spell mastery yet?
Here's the first draft of my spell mastery house rules. They're a bit clunky, and I'm open to suggestions on how they might be improved. Here goes:
Magic-users can achieve spell mastery. Any spell memorized by a magic-user can be replaced at will by a mastered spell of the same level or lower.
Magic-users who wish to master a spell must first find a mentor. Mentors are hidden mysterious beings - ancient, inhuman, possessed of alien intellects and appetites - that seek to advance their own goals, which most mortals find inscrutable. (None are of lawful or chaotic alignment.) Those that dwell in the material world are invariably found in inhospitable, near-inaccessible locales. Others must be entreatied in the otherworldly realms where they reside, be they nightmarish hells of impossible angles or gauzy opiate dreamlands. Though no two mentors are the same, they are universally temperamental and notoriously difficult to approach, each one first requiring a particular set of cryptic gestures, obscure passwords, outre offerings, etc. before any requests are entertained.
Furthermore, no mentor knows all of the spells in existence. (For example, Three-Headed Oul-Balam grants mastery in spells dealing with visual illusion and invisibility, while Glatth, Eater of Doves gives instruction in spells of travel, movement, and teleportation.) To research the means of finding a mentor capable of teaching mastery in a specific spell requires a significant investment of time and money.
The first time a magic-user attempts to find such a mentor, he must first invest 1500gp per spell level and one week per spell level desired, then roll under or equal to his Intelligence score on 4d6. Subsequent visits to a mentor who the magic-user has previously contacted cost 750gp per spell level, and the Intelligence check is made on 3d6. If the Intelligence check fails, the money and time are lost, and the magic-user must start again. If the Intelligence check is made, the magic-user has successfully contacted the mentor, and the chart below is consulted.
(The money and time represent mystical research of the proper etiquette, the purchase of the required offerings, and either an expedition to whatever inhospitable place the mentor inhabits, or the rituals - magical, drug-induced or otherwise - necessary to visit an otherworldly one. At the Labyrinth Lord's option, the costs in time and money may be waived if the magic-user and his PC companions agree to undertake an adventure in search of a hidden mentor.)
Spell Mastery Attempt Table (2d8) For a particular mentor, each roll below 12 provides a cumulative +1 modifier to future rolls on the table, until the result is 12 or higher. Once a result of 12 or higher is rolled, the modifier is reset.
2-3 What is the meaning of this? PC has offended the mentor somehow. Roll on the Spell Mastery Mishap Table below.
4-5 This should suffice. Mentor teaches PC a new spell of the Labyrinth Lord's choice. New spell is of the level in which mastery was desired, but is not mastered.
6-8 Is this what you seek? Mentor grants mastery in one spell currently known to the PC, but not the one the PC wanted (Labyrinth Lord's choice). If none of the PC's spells are those in which the mentor can teach mastery, see "This should suffice", above.
9-11 What have you done for me lately? Will grant mastery in exchange for a favor from the PC. Roll 1d6: (1-2) valuables (3-4) magic (5-6) mission. (The Labyrinth Lord should make the cost proportionate to the spell's power.) If the PC is unwilling or unable to pay the price, see "Get thee gone" on the Spell Mastery Mishap Table for consequences.
12-14 Very well; I shall show you the way. Mentor grants mastery in one spell of the PC's choosing.
15-16 You have long been a favorite of mine. Mentor grants mastery in two spells of the PC's choosing, and marks the PC physically in some fashion. (The Labyrinth Lord should devise a physical change that relates thematically to the mentor.)
Spell Mastery Mishap Table (2d6)
2 This I command. Mentor places a quest or geas spell on PC (no saving throw). Even if the mission is carried out successfully, mentor will not grant mastery.
3-5 The stars are wrong. Mentor refuses to grant PC audience. PC can try again in 1d8 weeks.
6-8 Get thee gone. Mentor ejects PC from premises and will provide no aid for 2d4 months.
9-11 Darken my door no more. Mentor casts PC out, will never be found by PC again.
12 I must despise you now. Mentor casts bestow curse on PC (no saving throw) and drives the character out, never to be found by PC again.
(These tables are based in part on Jeff Rients' "Suffer Fools Gladly" table in Fight On! #3.)