Your rogue and arcane training complement one another.
Benefit: Choose one arcane spellcasting class. Your caster level for that class increases by one for each level in the rogue class you possess, up to a maximum of 3 higher than your actual spellcaster level. In addition, when you become able to cast 3rd-level spells with an arcane spellcasting class, your sneak attack damage increases by +1d6.
Special: If you have fewer than 3 rogue levels when you take this feat, and later take additional rogue levels, your caster level continues to increase. This increased caster level only benefits the power of the spells you cast: for all other purposes, such as qualifying for feats, your caster level is still equal to your actual spellcaster level. This feat has no effect on which spells you know or how many you can cast per day.
Undefeatable: The Collected Feats Sourcebook, Copyright 2009 – 2010, Louis Porter Jr. Design, Inc. Undefeated, Copyright 2011, Louis Porter Jr. Design, Inc.