Mellisande, suddenly finding herself awash in gnolls, ducks away to get some breathing space, scrambling under wild swings from maces and jumping over scrabbly-clawed kicks until she's a bit more in the clear.
Then, with a wary eye on the single gnoll still looming over her, she sweeps her hand and intones, "SLEEP!"
(Shift to Q9 and cast Whelming Burst centered on the corner of M/N, 10/11. That should threaten all four gnolls there. Gnolls are blind, I don't think they get AoO's, right? Will save DC 18 or take nonlethal damage. Negated on success.)