When creating a new character who starts at a higher-than-first level (replacement character, high-tier campaign, etc.), are there recommendations on how many corruption points they should start off with? Ideally, I would want some sort of gambling mechanic where a player can choose to start with more corruption points in exchange for more XP or magical items.
They certainly should start with a number of corruption points equal to their number of black magic spell levels.
Beyond that, here's some gambling mechanics:
1. Characters typically have a 5% chance per level of magic items in each category. You could allow them to increase their chance for magic items by a number of percentage points equal to Corruption taken. For instance, if I am 5th level I have 25% chance of a magic item in each category. If I accept 15 corruption points, I can increase that to 40% in each category.
2. You could give them a chance of a necromantic magic item equal to 2 x the number of Corruption taken. For instance, if I accept 20 starting Corruption I have 40% chance of a necromantic magic item. The item should be worth no more than 5000gp per character level.
3. Have the player bid between 1 and 10 corruption. Roll 1d10. If the die roll is equal to or less than the amount of Corruption, he gains bonus XP equal to that percentage. If the die roll is greater than the amount he bid, he gains no XP. Either way he gains the Corruption. For instance, I am starting a new occulist with 8000 XP. I bid 7 corruption. Now I roll 1d10. On 1, I get 1% XP (80). On 4, I get 4% XP (320). On 7, I get 7% XP (280). On 8-10, I get no XP. I get 7 Corruption regardless. The player can repeat this process once per level before play.
I haven't done detailed mathematical analysis on any of the above - I'm just riffing in response to your "gambling" request. Hope it helps!
Anything - anything - that tempts players to accept Corruption on the characters is a plus to a game that uses Corruption. Corruption should be tempting.
The ideas in this thread hit that theme squarely, and with great flavor. Thanks folks!