Cooperative Magic
By your powers combined...
So an off-the-cuff comment of mine in another thread inspired Swicord with an awesome idea! Full-blown cooperative magic between channelers and/or heroes.
GW Swicord:
This initial brain-storming already suggests that there could be various types of cooperative magic. Raising something like a Bifrost Bridge would require direct and intimate cooperation and coordination between two channelers, while removing an offending overland enchantment could be accomplished by several channelers working towards the same goal, but not necessarily as one (though this could also be accomplished in direct cooperation). In the latter case, it could be something that happens naturally behind the scenes (although it could also potentially be arranged diplomatically). For the former, there could be a 'cooperative magic' tab in the diplomacy screen where everything could be arranged (this could be made more or less involved, based on popularity, difficulty of implementation, and depth of the magic system as a whole). For example, it needn't be an even divide - one channeler could invest more than the other; cooperative spells could be broken down into components, and different channelers might be better at some components than others (a fire-oriented channeler might be able to complete a largely fire-school component of a spell faster and cheaper than a life-oriented channeler).
Another type of cooperative magic could be channeler-hero and hero-hero magic. This could encompass a huge range of possibilities. It could be used to cheapen teleportation (the downside of cooperative teleportation is you'd need a decent magic-user at both ends of the spell), strengthen one party or the other, or boost the spells of one with the help of another. Costs would usually have to scale with distance, so a Channeler boosting a distant hero's spell might not be as efficient as a hero boosting an adjacent hero's spell.