:All right:
The ones that can get past him are mostly the ooze kind that can totally ignore levinbolts or fire and slip right under the door. And compulsions are slow, especially as he starts to tire; he prioritizes the insubstantial creatures, those seem pretty hard to stab. There are some monsters that look almost as though they're made of molten metal, or maybe just liquid mercury, shifting and reforming into amorphous limbs and eyestalks; the shield doesn't stop those either.
It's getting harder to tell what's going on outside the door, even with scrying; there's a pall of smoke over everything, from the burned bodies of creatures he had to set on fire because they ignored lightning, and there's also just a lot going on, as new arrivals fight over the dead before flinging themselves at the shielded door.
Eventually - gods, how long has it been, a candlemark? a day? five minutes? he can't tell anymore - something very big shows up, with too many jointed limbs and teeth in places that should really not have teeth and a mind too simple to compulsion. It takes down his entire shield. The snapped threads of magic rebound on him, ouch - and he has to frantically try to pin it in a force-net while he pummels it with enough levinbolts to stun it. And then frantically weave together the shield again. He throws up a thin wall of flame in front of the door, in the interim, but he's way too busy to try to stop the half a dozen smaller monsters that make it through that and claw their way under the door, most of them slightly on fire but apparently unperturbed.