Battle Mage Tactics( Monster Manual V, p. 84)
Through intense training and impeccable timing, you and your allies learn to augment each other's magical attacks when you focus your efforts on a single target.
Arcane caster level 3rd, Spellcraft 6 Ranks,
Each time you cast a spell that requires a target to make a saving throw, that target gains a battle magic tactics token after the spell resolves. A creature gains a token whether the creature succeeds or fails, but a creature that avoids a spell through spell esistance does not gain a token. Each battle magic token imposes a cumulative -1 Penalty on saving throws against the spells of spellcasters who have this feat. At the end of the round all battle magic tactics tokens dissapear.