One time you can easily use one specific metamagic.

Prerequisites: Base Casting Attribute 25+ or 23+ and another attribute base attribute 23+, Metamagician, Skill Focus(Knowledge Arcane)

Benefit: When selecting this metamagic feat choose one metamagic for which you have the metamagician feat. This feat grants one of two effects, that you choose when you are preparing the spells:

• Sudden Metamagic: Once per day as when casting a spell you can enhance that one spell with the metamagic feat and ignore up to four levels of increase. You cannot combine that one spell with any other metamagic. This feat uses up your swift action if the spell does not already do. You can never reduce the spell-slot cost below the spell's actual level.
• Constant Metamagic: When preparing or casting a spell modified by that metamagic feat, lower the spell-slot cost by one. You can never reduce the spell-slot cost below one the spell's actual level. This effect does stack with other reductions.

Special: You may learn this feat multiple times each time for another metamagic feat. Its effects stack.