Characters will earn points each time they play. Ways of earning points: showing up, role playing, turning in a good note, playing cleverly, helping other characters, advancing your allies' goals, and so on. Typically, three to five points will be earned per game. If a particularly important event takes place, this can be as much as seven or more. New characters, and those who haven't played since this system was implemented, each get 5 points to start with.
You can earn points in back time. If you choose to burn the time without doing anything in particular, I will give you one point per month. If you do something productive, I will give two per month.
RATINGS
Ratings can be improved at the expense of current rating times 1. Maximums of 18 will apply, unless the character has all seven ratings within two; then they can be exceeded. For instance, if you have all 17 and 18 ratings can spend the points to get a 19, but can't get a 20 until all ratings are 18. Strength will be improvable one category at a time from 18 to 18:00, costing 18 points per each step. (Note this was updated 2014/03 to remove the phrase about 'racial maximums', which I do not use.)
Note that if a character with an exceptional (18:01 to 18:99) strength rating that is not at the top (such as 18:79) spends points, they must first increase the rating to the top of the current range, costing a prorated amount of CIPs (rounded mathematically), but never less than 1 CIP.
If a rating is otherwise somehow a partial point (such as a constitution of 17.3), then the cost will be whatever fraction of a point that is needed (in this case, 70% of 17, or 11.9, rounded up to 12) - it is not possible to spend CIPs to increase a rating to any non-round number, except in the case of exceptional strength, above.
HIT POINTS
A hit point can be bought for 2 character improvement points. Multi-classed characters can apply them to whichever class they choose. The only limit to this is "perfect" hit points, as if the character had always rolled maximum on all hit dice.
PROFICIENCIES
A character can purchase a weapon proficiency for a number equal to the current number of weapon proficiencies times 1 (but never more than 10 points). A specialization can be bought without using additional proficiency slots at a cost of 15 experience points, assuming the character is proficient with the weapon already, and only for qualified characters (fighters, rangers, etc.). Double specialization will cost an additional 15 points, and bow (etc.) specialization costs 30 points. Nonweapon proficiences may be purchased at the rate of current nonweapon proficiencies times 1, excepting those which are listed as costing two proficiency slots, they cost current nonweapon times 2. The upper limit of each (weapon and non-weapon) is the character's intelligence or wisdom, whichever is higher. [Note this is just a simple count of proficiencies; the ones that cost 2 points to learn only count as 1 when comparing to intelligence or wisdom.] However, it will never cost more than 5 points to buy a non-weapon proficiency, except those which would normally have cost 2 points; they will max out at 10 points.
[Note - magical enhancements to your number of NWP do not count against your upper limit - this would include items such as the Tablet of Horus, and the Spire of Center.]
LANGUAGES
Languages can e bought at a cost of current number of languages known times 1, with a maximum cost of 5 points (regardless of number of languages known). The upper limit is equal to the character's intelligence.
SAVING THROW BONUSES
A saving throw bonus which applies to all attacks in a particular column of the saving throw table can be bought. The cost is 5 times current bonus, and 5 for the initial +1. This cannot exceed 5 in any case. Also, see Psionics below for a special note on psionics saving throws.
COMBAT BONUSES
A 'to hit' bonuses can be bought for 10 times current bonus, with an initial cost of 10 points. The maximum for this is +5. This will apply to one specific weapon, although the bonuses can be bought for more than one weapon. Similarly, 'on damage' bonuses can be purchased under the same rules.
THIEVING ABILITIES
Thieving abilities can be improved at a cost of 2 points per percentage point; this 'bonus' will be recorded separately. A similar bonus to assassination percentages can be bought at the same rate. The upper limit is the 'natural' percentage plus fifty. The backstab multiplier can be improved at current multiplier times 10. The upper limit is still 5 times normal damage.
PSIONICS
Psionics can be purchased for 20 points. (Note this does not grant any abilities - they much be purchased, as follows here.) Abilities can be purchases for 10 points per lesser, 20 points per greater, and 30 points for grand abilities. Attack and defense modes can be purchased for 10 points. Three lesser abilities must be possessed (whether gained naturally or through purchases) to purchase a greater ability, and two greater abilities must be possessed to purchase a grand ability. Levels of mastery can be purchased on existing abilities just as if the character were buying the ability new. However, the level of master of a greater ability cannot exceed that of any lesser ability, and ditto for greater/grand abilities. Psionic strength points can be bought at a cost of 2 points per strength point, with a limit of plus fifty.
A non-psionic character can purchase a psionic saving throw in the same manner as listed for other saving throws; this will lower your psionic potential each time it is done. This saving throw cannot exceed +5. A character can "move" his psionic potential anywhere in the range between resistant (potential of 30 and below) and naturally psionic (somewhere between 90 and 100) at an expense of 20 points. If the character is psionically resistant (below 31), he must negate the saving throw bonus in reverse of the above method before he can otherwise alter his potential.
SPELLS
Magic-users and illusionists can automatically learn a spell that was 'missed' at a cost of 1 point per spell level.
**UPDATE – APRIL 9 1998**
Spell casting characters may buy the ability to cast additional spells (beyond what the class/level tables allow, with wisdom bonuses as they apply) at a cost of 5 times the level of the spell. The maximum allowable base spells per day (not counting wisdom bonuses) is the character’s intelligence (for MU and ILL) or wisdom (for CL or DR). Character such as rangers and such can also do this, and use intelligence or wisdom as per what sort of spell they are ‘buying.’
UPDATE - AUGUST 2022
Much like the thief ability section above, other classes with skills that require percentile die rolls can buy improvements to this skills. Such improvements cost 2 CIPs per percentage point, and such skills cannot be raised more than 50 points in this manner. This includes, but is not limited to, Ranger tracking, Monk mental resistance (see PHB page 31, paragraphs B and G), and Bard charm and legend lore/item knowledge. I've probably missed some other similar items, so if you think of any that seem similar, let me know.
NOTES ON NOTES
A good note will earn you points, but please remember - a long, wordy note is not a good note! A good note tells me what you used up (particularly magic), what money you spent, what you bought, what you traded, what clever things you did. I don't need to know every action you took, what damage you took or dealt, or what spells you memorized or cast, in general. Please put your character name on the note. You can safely assume that you pick up anything you shoot or throw that is not destroyed except under unusual circumstances - shooting while fleeting, the item falls into a pit, or something similar.
FINAL NOTE
I made this system generous on purpose. I want the players to have fun and tailor their characters. The limits should prevent the system causing characters from becoming juggernauts. If I do change the system, it will not be retroactive, except to your benefit. I tried to cover all the possibilities, but please let me know if you have any additional ideas.