You are able to synthesize lesser magic and cast multiple spells from different sources at the same time.
Benefit: You can cast two spells, one from each of your spellcasting classes, as a full-round action. Both of the spells must have a casting time of no more than one standard action and they must have the same casting time. Additionally, the spells must be no higher than 2nd level. You can make any decisions concerning the spells independently. You can use this ability a number of times per day equal to one third of your mystic theurge level, in addition to the spell synthesis ability you gain upon attaining 10th level of mystic theurge.
Undefeatable: The Collected Feats Sourcebook, Copyright 2009 – 2010, Louis Porter Jr. Design, Inc. Undefeated, Copyright 2011, Louis Porter Jr. Design, Inc.