I've been thinking on Cooperative Magic in order to get that cinematic feeling of the frontliners defending the casters in clutch situations and big scale magic retinues on a battlefield. It could replace spell scrolls entirely with formulas for this casting in harder settings.

Cooperative Magic allows a group of spellcasters to cast a spell they couldn’t otherwise, and to combine their talents and resources. To cast the spell, they must contribute spell slots to build up to the power of the target spell slot. Two spell slots of level n combine to produce level n+1 (so four nth-level spell slots to produce n+2, etc). Contributing a spell slot requires an action and concentration. If a spellcaster’s concentration is broken before the combined spell is cast, the spell slot they contributed is lost, and also the rest of the spellcasters take a penalty to concentration. Once enough spell slots have been contributed, casting the spell requires another action (and concentration has to be maintained until then) by one of the members of the group. The final, combined spell is not only higher-level than any of the spell slots they used, but also benefits from all of their feats, features, and metamagic.

Really a situational casting, but it's there; forces at least the expenditure of a whole turn to feed the slots during combat, and it gets those tense scenes. It allows low lvel casters to be useful in big casters spells. It allows low level casters to pool their resources and cast higher-than-known spell scrolls they find. Also allows casting 7+ spells more than once a day.

How balanced/overpowered would that be?

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    \$\begingroup\$ What is your actual question? The Q&A format here works best when you have a specific question that can elicit specific answers. \$\endgroup\$ Oct 9 at 5:04
  • \$\begingroup\$ Right now, your question looks a lot like idea generation with your last paragraph asking for "some feedback and some other options" - I suggest that you remove your section and ask specifically about your 'cooperative casting' concept. Remove all after "My current ideas" and close with "is this within balance" or words to that effect. That will keep your question in scope and it will provide a chance to answer your concern "does this change the power/balance in detrimental ways" (Which I think is your problem you want to solve. Did I guess correctly about that?) \$\endgroup\$ Oct 9 at 18:57
  • \$\begingroup\$ Quite aside from this being idea generation as some others have said, this is very 'cart before the horse' as you are asking us to set aside some fundamental aspects of your theory. Is this perhaps a 'cool idea' that you haven't thought through properly yet? \$\endgroup\$
    – SeriousBri
    Oct 9 at 22:23
  • \$\begingroup\$ I rewrote this in a more “rulesy” style, which may help others read it. I’m fairly confident in everything about what you’re proposing, except for two things: what penalty is applied to the other members of the group when one’s concentration is broken, and the action to cast the final spell, does that require an action from just one of the group, or does it require an action from everyone in the group? Your write-up was unclear on those points. \$\endgroup\$
    – KRyan
    Oct 10 at 13:59

This is unlikely to be useful by player characters in combat. Two level-N spells are just better than one level-N+1 spell, especially when you consider that it's going to take minimum three actions to cast it. (If I'm reading your text correctly, the caster who spends an action to cast the spell has to be someone who has already contributed a slot to it.) Including all the feats and abilities of the participating casters is nice, but won't change the math overall.

It's hard to know if this will be useful by NPCs in combat. You've described a situation where a single high-level caster is combining the spell slots of many lower-level casters, and that sounds very cinematic. But if you had lots of low-level casters with slots, they could just all cast magic missile at once, and the damage from that is probably higher than whatever cooperative spell they were going to cast.

There's a question here about spell knowledge. Suppose we have four casters who can cast spells up to level N, and they really really want to cast a spell at level N+2. None of them is eligible to prepare that spell. Are they just out of luck, or is there a mechanic for preparing a spell that you couldn't normally prepare, if you're planning to cast it cooperatively?

If there is a way to prepare and cast that level N+2 spell, then this is really useful for both PCs and NPCs, for casting spells that would otherwise be unavailable. For example, PCs could combine their skills to cast a teleportation circle which they couldn't otherwise have managed, or NPCs could cast antimagic field or banishment at a key moment in a magical conflict. If there's not a way to do that, then cooperative spellcasting is much less useful overall.

A final note: the thing you're describing here sounds like it's mostly intended for NPCs. Remember that NPCs do not have to follow the same rules that player characters follow. If I wanted to produce a cinematic thing like the one you're describing, I'd probably create a custom NPC class called "support mage", and I'd narrate that this class could stand next to a caster and buff their spells and use reactions to defend against incoming attacks. That would accomplish the goal of looking cinematic, without the worry of having to deal with balance issues if the PCs tried it.

  • \$\begingroup\$ Knowing that accessing spells not otherwise available make it more compelling gives me good ideas for a new setting I'm working on. I think I'll go that route. I was never really aware of the maths behind the spellcasting, but this made it clearer for me. Thank you! \$\endgroup\$
    – BasnetI
    Oct 11 at 22:36

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