Sacrificial Magic

[Babale]

I'm planning to DM a campaign set in a Mesoamerican type setting, and had the idea of replacing the standard casting system with some sort of sacrifice-based system. The idea is, casters would have a set of spells known, but to actually cast a spell would require a worthy sacrifice -- small animals will suffice for low-level spells, but high-level spells will require humanoids to be slain.

I'm trying to come up with a good way to model this. I'm tempted to learn from the Psionic power point system, and have the spellcasters slay a certain HD's worth of living beings (or for some spells, sentient beings) in order to cast a spell. But the issue is this -- how many commoners should a sorcerer have to kill (by hand, of course) to cast Meteor Swarm? 9 doesn't seem unreasonable; but 9 commoners is chump change in comparison to Shapechange (even if we agree that Shapechange should not grant this caster free SLAs). I suppose that's true for using up spellslots, too, but it's even more pronounced here.

So if you were trying to come up with a system to force casters to sacrifice living creatures to cast their magic, how would you do it? A modified Spell Seed system? Burning HD for magic?

[Tvtyrant]

I would probably either use the rules from Book of Vile Darkness and have them use those in addition to other spells, or use a normal system but require a sacrifice to recover slots/power points.

[Bullet06320]

for a Mesoamerican type setting try looking into Maztica
http://forgottenrealms.wikia.com/wiki/Maztica_Campaign_Set
they gave it away for free on the WOTC site, but all the links I found no longer work to the free download

http://www.forum.candlekeep.com/topic.asp?TOPIC_ID=19368
that is some very good fan works for Maztica all in 3.5

Dragon 315 also has updated Maztica info

[NevinPL]

If you want to make sacrificing creatures a not so easy process, you should probably base it on CR, not HD, or on both of them.
0 level - sacrifice animal or a sentient of at least CR 1/2
1st level - sacrifice animal or a sentient with at least 1 HD, and CR 1
2nd level - sacrifice animal or a sentient with at least 3 HD, and CR 3
3nd level - sacrifice animal or a sentient with at least 5 HD, and CR 5
[...]
8nd level - sacrifice a sentient with at least 15 HD, and CR 15
9nd level - sacrifice a sentient with at least 17 HD, and CR 17

It needs fine tuning, especially in the HD area, but I think you get the message.
You can also play with the improvements "excess" HD and\or CR can do - you sacrifice a CR 5 for a 1st level spell, you have 4 levels for metamagic. Or how sacrificing a sentient when an animal will suffice, also improves the spell (caster level for example).

[mabriss lethe]

It depends on how useful you want this magic to be. If you want it to be something viable for player scale adventuring, you'll want to make it a token sacrifice. If you want to reserve sacrifice for out of combat scenarios follow something akin to the previous posts, with perhaps a few caveats. Something like : sacrificial magic eases or negates the personal cost of casting magic. Use the above guideline for prepared caster classes. Spontaneous casters may use lesser sacrifices to reduce the level of spell needed by given amount. You could alternately make sacrifices a form of magic used solely by non-casters.

[ComaVision]

You could use the Incantations spell variant from Unearthed Arcana (http://www.d20srd.org/srd/variant/magic/incantations.htm) as a framework.

[Flickerdart]

You could give all casters a Circle Magic type mechanic - every being a caster sacrifices gives him bonuses.

[The Viscount]

Death Master has a small subsystem in its casting for using vials of blood harvested from creatures. It's pretty simple, you might want to tweak it if you want casting from sacrifice to be easier or harder.

[frogglesmash]

If you want to make sacrificing creatures a not so easy process, you should probably base it on CR, not HD, or on both of them.
0 level - sacrifice animal or a sentient of at least CR 1/2
1st level - sacrifice animal or a sentient with at least 1 HD, and CR 1
2nd level - sacrifice animal or a sentient with at least 3 HD, and CR 3
3nd level - sacrifice animal or a sentient with at least 5 HD, and CR 5
[...]
8nd level - sacrifice a sentient with at least 15 HD, and CR 15
9nd level - sacrifice a sentient with at least 17 HD, and CR 17

It needs fine tuning, especially in the HD area, but I think you get the message.
You can also play with the improvements "excess" HD and\or CR can do - you sacrifice a CR 5 for a 1st level spell, you have 4 levels for metamagic. Or how sacrificing a sentient when an animal will suffice, also improves the spell (caster level for example).

The problem with this system is that being a caster basically requires you to lug around a veritable zoo of animals and makes it incredibly impractical do adventuring of any sort.

[NevinPL]

The problem with this system is that being a caster basically requires you to lug around a veritable zoo of animals and makes it incredibly impractical do adventuring of any sort.
Preaching to the wrong poster.

[Babale]

You could use the Incantations spell variant from Unearthed Arcana (http://www.d20srd.org/srd/variant/magic/incantations.htm) as a framework.

The idea I ended up going with was very much inspired by this. I created a system where every spell has a cast DC -- in very broad terms, 11 per level. In order to lower the 99 DC cast for a 9th level spell (with the added caveats that spells do not scale by default and making them scale adds to the DC) you can sacrifice creatures, with humanoids being worth more than others.