Spell Thief

[Luphey]

From what I remember about spell thief, you needed to successfully attack someone who is casting a spell and if you land the attack you stole said spell(pathfinder). But i think also, you could sneak attack someone and forgo the damage to steal a random spell from their spellbook(3.5). So I think if this was an archetype it would fit better with thief. But the spell casting per day for spell thieves was also not very impressive(4 per level at level 20).