Dual Focus

Countless hours have been spent training your mind to maintain focus on concurrent incantations, taxing as the process may be.

• If you attempt to cast a spell that requires concentration while already concentrating on an existing spell, you can maintain concentration on both spells simultaneously. You must spend a standard action each subsequent round on maintaining this concentration, or lose concentration for both spells.
• At the end of each turn where you have two spells you are concentrating on, you must make a Constitution saving throw (DC equals 10 + the number of complete rounds you've been concentrating on two spells). On a failure, you lose concentration for both spells. You can drop concentration on one of your spells during your turn as a free action to avoid this saving throw.
• Any time you would be forced to make a Constitution saving throw to maintain concentration due to taking damage, the DC equals 10 + both spells' levels combined, or half the damage you take, whichever number is higher. On a failure, you lose concentration on both spells.

-Tal'Dorei Campaign Settings p.108