Yet another metamagic feat to ponder

[Dalcassius]

I've always thought that if a wiz/sor can bring vast powers into existance with naught but a few gestures and words as easily as a seamstress works linen, then why can they not a simply undo that which they have wrought.

So...

Dismiss Effect
You can undo the power you have brought into effect, haulting its continued progress.
Prerequisites: Extend spell plus any one other metamagic feat.
Benefit: You are able to end a spell before its duration has run its full length. This feat only effects spells that have a duration which isn't instantaneous, permanent or already marked with "(D)".

I'm sure there is something I'm missing so I was hoping you all could point any blatant flaws I've ignored.

[ILM]

Well, you kind of forgot the spell level adjustment.

[Dark]

This sounds like it could be hilarious when applied to Water Breathing.

If you're CN, that is :)

[Grey Watcher]

Frankly, I don't see why it needs any prerequisites. Essentially, giving you the power to end your own spell-effects before you've gotten the full benefit of them could easily fall under the category of metamagics that don't need prerequisites or level adjustment. I mean, I can't think of any instance where you might willingly end a spell effect early. Unless maybe you're using Symbol of Pain as a torture device or something.... Or you could end debilitating spells early in the event an enemy surrenders.

[valadil]

I always played that you could do that anyway. Although it doesn't come up that often, sometimes you just gotta drop that wall of force to clear up the battlefield.

[HempRope]

I think that it certainly should require some discipline, and so there needs to be a corresponding feat, and also that it is important (in case you cast Wall of Fire and the enemies get through it, and persuit is imperative...).

However, I don't think it's exactly a metamagic feat. Because you don't, in the original casting of the spell, cast it as "dismissable." It more affects the spellcaster than it does their spells.

I think the Prereqs are fine, as the caster might need practice manipulating arcane energies, but those might be harsh. Perhaps just a minimum caster level would be suitable, or merely one Metamagic feat.

As a note, there is an Archmage ability that's very similar, except that you're allowed to bring the effect back after you've dismissed it.

[Dalcassius]

At first I was thinking of a +1 LA for the spell level, as few metamagic feats let you get by without one. However after so thought and some good points here, I think it shouldn't apply any LA at all.
The other thing that people have mentioned is the pre-reqs. They seem to be a little intense for a feat that isn't all that impressive or powerful. Perhaps just a min spell level required. 3rd level maybe? It is when a non-human wiz/sor would be getting their second feat, so it balances out against needing one specific or one generic metamagic feat.

So we've got (with edits in italics)...

Dismiss Effect
You can undo the power you have brought into effect, haulting its continued progress.
Prerequisites: Caster Level 3rd or higher.
Benefit: You are able to end a spell before its duration has run its full length. This feat only effects spells that have a duration which isn't instantaneous, permanent or already marked with "(D)". There is no spell level adjustment for this feat.

[Darkie]

Something like this could be useful... and not having LA is good for having to spend a feat for this.

Last week Sunday, my party's Artificer finally got Chill Metal off on a warforged. My warmage then demolished a few enemies, and the warforged surrendered... and then the chill metal finally kicked in. Since it wasn't dismissable, the artificer had to cast Heat Metal on our prisoner to keep him from dying.