A GM I played with used to rule that a quickened spell always reduced the casting time of a spell by 1 round, and reduced a 1 round casting time or a standard action casting time to a swift action, and a swift action to a free (or immediate, he was somewhat inconsistent) action.
Thus I only recently realized that RAW, quicken only does the second to last of those things (standard or 1 round to swift)
If I, as a GM, were to attempt to find a balanced way to allow players to metamagic their spells into immediate actions, what level of metamagic would that be? My thought so far is to create a new metamagic feat that allows you to turn a swift action casting time into an immediate action casting time – thus, it stacks with quicken (so I don't have to deal with rules about applying the same metamagic twice), and forces casters to commit two feats if they want to double-quicken their spells into immediate actions.
But if I do it this way, there's nothing that a priori says this new metamagic feat would have to also be a +4 spell level feat. So, my question is… what's the ability to make a swift-action spell immediate worth, in terms of spell-level adjustment?
Best Answer
This cannot be balanced
The power you suggest would be immense. It would open a wealth of exceedingly powerful options to the already-most-powerful classes. The ability to act more than you are supposed to, à la Quicken, is one of the most powerful abilities in the game – but it falls well short of being able to act when you shouldn’t be able to act at all – which is what you propose.
This metamagic feat would be close a super-contingency, and contingency may very well be the most powerful spell in the game, limited only by the fact that you can only establish a single contingency at a time. With this, you can make as many spells as you like contingent, and you don’t even have to set the trigger ahead of time, you can just react immediately. In 3.5, there was a Craft Contingent Spell “item” creation feat, which was very-frequently banned, even in the highest optimization games, as one of the most overpowered options in the game.
There is no price you can put on this that wouldn’t allow someone to break the game. Even if you literally gave it a +10 adjustment, making it impossible to use under normal circumstances, someone would find a way around the cost. Magical lineage and metamagic master traits, spell perfection feat, or even just a simple metamagic rod.