A friend's build

[Cranthis]

One of the players in my group is having me help with his build.

He is going Spellthief 1/ Wizard 5/ Spellwarp sniper 10 http://scratchpad.wikia.com/wiki/Spellwarp_Sniper

Now he needs something to close out with. He says that the sneak attack is only as a side thing. Casting, and sneak attacking when able, but not focusing on it.

He would also like to focus on electric energy magic.

Yes, I told him about Energy Substitution.

Edit: He is already level 6, so Spellthief 1/ Wizard 5 is locked.

[Mightypickle]

I believe Unseen Seer from Complete Mage could fit in nicely. Your friend will continue improving his casting and his SA damage, and it's really easy to qualify for. You also get a semi-useful feat (silent spell) and good skills (6/level).

There are probably better PrCs out there, but Unseen Seer is a fun, if simple, answer.

[Cranthis]

I have allready recommended Unseen Seer, Arcane Trickster, and Magelord to him. He just wants a few more options

[Biffoniacus_Furiou]

Paragnostic Apostle is quite good. Master Specialist could be useful depending on his specialization, if any. Incantatrix is the go-to for power. Divine Oracle can get him Evasion and Uncanny Dodge, and he can get its feat prerequisite by visiting the Frog God's Fane in CS. Fate spinner could be useful. Abjurant Champion is even a useful choice, though extremely late in the build.

[eggs]

The homebrew half of that class looks like it opens some fun options for a buffer (combine with Ocular Spell for War Weaver Lite + sneak attack).

Snowcasting + Flash Frost Spell + Born of the Three Thunders would let you do things like sneak attack select targets with an electric Antimagic Sphere (I frankly have no idea how that would resolve, but I'm sure it would be neat).

The thing I'd look at would be Spellguard of the Silverymoon (4 levels of which fit very nicely in there), to share things like Shapechange with the entire party (or if that's too generous of a reading, dragonshape on a bunch of mooks could be fun; requires Ocular Spell and Midnight Metamagic) or to do things like hit 10 enemies with Ocular Tenser's Transformation (no-save casting/magic item shut-off switches? Hilarious).

Alternatively, anything with free/cheap metamagic (http://brilliantgameologists.com/boards/index.php?topic=9876) or extra metamagic feats would probably do more to improve electricity-themed casting than most specialist elemental casters.