Well, there are no denying the benefits that a rogue/arcanist can get from skill synergies with a familiar, but a familiar is the appetizer, not the entree. Dungeons and Dragons success often means hitting hard and often -- and for a rogue, that means making effective sneak attacks. The sweet spot of the arcanist/rogue combination is using magic to maximize those attacks.
But first, a primer on sneak attacks, and when you get to make them. This series of articles on sneak attacks is a great place to start. To sum up, a rogue gets sneak attack damage when:
- He is flanking a foe.
- He is unseen, so that his foe is Denied Dex Bonuses (DDB).
- His opponent is blind, so DDB.
- His opponent is grappled by someone other than the rogue, so DDB.
- His opponent is surprised or flat-footed, so DDB.
How can spells help with any of those?
Flanking: First, your familiar can flank. However, a tiny creature (with reach 0') cannot flank. So you either have to enlarge your familiar first (a shared Enlarge Person or Alter Self spell works well for this) or use the Improved Familiar feat to gain a familiar that is small size or bigger. Remember that both you and your familiar have the same ranks in Tumble, which helps in getting into flanking position.
Also, you can summon monsters into flanking position -- or your familiar can, by reading a Summon Monster spell or using a higher-end Bag of Tricks.
Unseen Rogue: The Invisibility spell is the archtype here -- but since you turn visible when you attack, only the first attack is a sneak attack. Greater Invisibility lets every attack you make into a sneak attack, but as a fourth level spell, that is not available to a multiclassed rogue/mage for quite a while. Blink is ideal for the same reason, and it is only a third level spell.
Another option is to snipe -- hide, then emerge, fire, and hide again. Even if you are being watched, you can do this by creating a diversion to hide. Check out the rules under the Hide and Bluff skills. Spells can help with this by creating something to hide behind (the Shrink spell can be handy in that) or using Darkness to hide in. A Glove of Storing can be useful in holding the object on which you cast Darkness: Hide in darkness, then, on your turn, store the Darkness object, attack, bring out the object, hide again. More simply, hide behind illusions -- if your familiar reads the illusion spell from a scroll, it can concentrate on the illusion as you fire.
Blind Opponent: The Glitterdust and Blindness spells are only second level, so they are winners for this. Pyrotechnics is a possibility, if you have a fire source and can get close enough without affecting yourself or allies. Color Spray can also do the job against weaker opponents.
Grappled Opponent: Use this by summoning creatures who are good grapplers, or with the Black Tentacles spell.
Other Notable Spells:Remember that any attack that requires a roll and does damage of any kind can be a sneak attack -- including rays and touches. Also remember to use those buffs: Expeditious Retreat, Shield, Mage Armor, Cat's Grace, Bull's Strength, and (best of all) Heroism.
With a little preparation, forethought, and the right spells, just about every attack your rogue/mage makes can be a sneak attack! (At least, when you are fighting creatures who are not immune to them!)
Edit [31 Jan 05]: I can't believe I forgot to mention Leomund's Tiny Hut! Known in the SRD simply as "Tiny Hut," this spell packs a surprising punch for the arcane rogue. Here's the money quote: "Missiles, weapons, and most spell effects can pass through the hut without affecting it, although the occupants cannot be seen from outside the hut (they have total concealment)." For a rogue with total concealment, every attack is a sneak attack! This is a great option for a rogue specializing in missiles. Just like Blink, but with no miss chance ... and your other rogue friends in there with you gain the same benefit. Sweet!