Ritual Spellcasting for Fun and Profit

This post over at Semper Intiativus Unum, while pertaining directly to older versions of D&D, seems to lay down a pretty good skeleton for what I want to accomplish in regards to my last post.

In it, Mr. Rossi puts forth being able to cast certain spells as rituals, which require quite a bit of time to cast, as well as material components of no meager amount.

Taking that skeleton, and the "basics" of the system presented there, let's see where we go with it...

Ritual Casting
Ritual Casting can be performed by any character with the time, resources, and courage to do so. As performing a ritual isn't the same thing as casting a spell, there is the risk of the magics going awry, failing completely, or drawing the attention of some outside force.

• Casters may cast any eligible spell that they could normally memorize, as a ritual, without memorizing the spell. No list will be given, but obviously, no combat spells may be cast in this manner, and all other spells will be handled on a case-by-case basis.
  
• Rituals take 1 minute to cast plus 1 minute per level of the spell being cast. If the spell the ritual is meant to emulate has a casting time of a minute or more, add this to the casting, in addition. Any interruption in the casting disturbs the spell and it cannot be cast again in the same day. (And possibly has mishaps.)
  
• Casting a ritual spell requires any given material components listed for the actual spell being emulated, as well as an appropriate offering/sacrifice, that could include blood, living or dead creatures, material possessions, etc. This offering will be decided by the player, and if not sufficient, may result in the ritual failing, or a mishap of some type.
  
• Any spell may only be cast as a ritual once per week, and characters may not in any case cast more than 3 ritual spells in one week, or more than one per day. However, if a player should want, they can push these limits, with a greater chance of mishaps and failure with each ritual casting.
• When casting a ritual, any character able to cast spells must expend a spell slot of a level equal to the spell being emulated in the ritual. Those performing a ritual who are not spellcasters, or who do not have spells of the required level, will be Fatigued for a number of minutes equal to the level of the spell emulated. In all cases, the caster of a ritual will be Dazed for a number of rounds equal to the emulated spell's level upon completion of the ritual.

In all instances, a ritual has a chance of failure. The base chance of success when performing a ritual is 30%, modified by the following:
+2% per character level
+5% if the spell emulated is on your class' spell list
+5% if the character performing the ritual is a caster of any type
+5% if the character performing the ritual is an Oracle, Sorceror, Warlock, or Witch
-15% per ritual cast over the 3/week limit
-15% per ritual cast over the 1/day limit
-25% for each ritual in a week emulating the same spell as a previous one in the week.

If a ritual success roll is failed by 25% or more, a mishap occurs. I don't have anything for this as of yet, but I want them to be colorful (and in some cases, very dangerous,) as the ritual performer is trying to skirt the foundations of magic...which, unless formalized by proper spellcasting is a very chaotic force.

Also, if a ritual is disturbed during casting, roll d% and consult the following table:
1-50: Nothing happens, and the ritual fails. The offering cannot be used again for another ritual.
51-78: The ritual fails and the energies powering the ritual are released with unpredictable results. This is left up to the DM, but defaults to 1d6 damage per level of the emulated spell to the caster and all within 5' per level of the emulated spell.
79-94: The ritual fails, and the caster must roll on the mishap table.
95-98: The ritual is completed, but the results are left to the DM. Roll on the mishap table.
99: The ritual has garnered the attention of some powerful force, be it an ancient evil, a god, or another extraplanar entity.
100: DM's Choice (though it should be exceptional)

Due to the nature of their connections to outside forces beyond normal ken, Oracles, Warlocks, Witches, and Sorcerors all add +5% to the above table and the mishap table.

I like this so far, as it's pretty simple and offers reward with some risk. I'm not sure what I want to do with the mishaps, but perhaps I'll use the Psychic Phenomena/Perils of the Warp tables in Dark Heresy as inspiration, and I'll probably look into the AD&D Tome of Magic's Wild Magic table.

More on that as it comes!

Edited 3/13/11 to change percentages of success and disturbance chart.