Impromptu Metamagic (3.5e Feat)
From D&D Wiki
Impromptu Metamagic [Psychic]
Prerequisite: any metamagic Feat, Psychomagic
Benefit: You can attempt to use a metamagic Feat "on the fly", without special preparation of the spell or an increase in its casting time. In addition to knowing the spell and the metamagic Feat you're trying to use, you must also be carrying an unused spell of the appropriate level (including the level increase for the metamagic Feat). If you need to prepare spells in advance, you must also be carrying the unmodified spell. Success is determined by a Spellcraft check with a DC of 10 plus twice the spell's modified level: if successful, you must sacrifice a spell of the modified level to power it. If the check fails, you can cast the unmodified spell if circumstances allow: alternatively, if you normally cast spells without preparation (and therefore already have the ability to apply metamagic Feats "on the fly" but with an increased casting time) you can still do this if circumstances allow. Otherwise the unmodified spell is considered lost (if you have it, the Spell Recovery power can be used to retain the spell, with a DC of 10 plus twice the spell's unmodified level). Use of this power with multiple metamagic Feats is permitted, but all the metamagic enhancements will fail together if the single check fails. For instance, an attempt to cast a quickened magic missile without preparation requires knowledge of the spell and the Quicken Spell feat, a prepared magic missile (if you need to prepare spells), a 5th level spell slot (possibly occupied by another prepared spell), and a Spellcraft check with a DC of 20. Success indicates that the quickened spell can be cast, using the 5th level spell slot. Failure indicates that the caster must immediately cast the spell normally, requiring a standard action and using the 1st level spell slot, or abandon the spell (wasting the 1st level slot). If the spell is abandoned and the caster has the Spell Recovery feat, the DC for recovery is 12.
Note: Related to Psionic Gifts Variant Rule