Just a quick note:
Sleep won't work (and at this level is a completely redundant spell). It only affects 2d4 hit die of monsters and monsters with critters who have more than 4 HD unaffected.
Sirene, however, has Domination memorized and Chaos. So she could sneak in under Improved Invisibility and cause merry hell.
My preference is, however, for blowing stuff up. I like to keep things simple.
