Gash opens a portal to the edge of the cave and Gish helps him drag the trolley of salt through.
L: Once they crossed over, I had to have faith in them. That's all I could do.
"Now what?" he asks, "Do we drag it around the cave? You think there's enough salt to go the whole way."
"Probably not if we're just pouring it," says his sister, "But I've got an idea." The worms nearest to them begin oozing in their direction. "You protect the salt; I'll make the circle."
Gish draws her scimitar and channels energy through the blade. She reverses her grip and runs, dragging the blade through the ground behind her. As she races around the edge, the worms from the mass launch their bile from the sky. Gish deflects the few in her path with a small energy shield and keeps moving.
Ahead of her, more worms crawl forth to block her path with mouths wide open. Gish channels energy through her gauntlet and punches blasts of energy right into the open maws. "Get!" Fire. "Out!" Acid. "Of!" Ice. "My!" Lightning. "Way!" Sound. The energy attacks stream out from her fist and explode inside of each target, disorienting them.
L: Gish once taught me her 'Five Fist Power Punch'. D: What's that have to do with the salt? L: I just mean, I knew she could defend herself.
As she continues to run, she thinks hard. What does she have that could draw attention away from herself? ...Herself? That could be it. She reaches into her shadow, faint as it is in the dim cave, and rips it out of the wall. In an instant, her shadow multiplies and scatter about; each 'her' racing off in a different direction, leading most worms away.
The majority of the undead horde's attention remains on the tower and its defenders, witnessing the desperate flinging of spells infuriates the tallgoblin. She has to work faster, she has to BE faster. She channels more energy into her legs, Stomping up a storm, ripping through the ground, leaving a trail of flame behind her, Gish pushes herself as far as she can.
She can see her brother's position again. He swings his axe, launching cleaving waves through the cretins approaching him. More crawl over their writhing split open brothers and some attempt to burrow under them; the latter being stopped by the metal plating that has covered the ground in Gash's location. There's still enough room behind it for Gash to complete the almost-circle.
As she approaches, another worm lunges for her. She pulls a pillar of earth up into it, the force flinging it head over tail back where it came from.
Gish keeps running, dragging her blade to complete the loop. As her blade reconnects with its starting point, she stumbles, trips, and rolls along the ground.
"Gish!" yells her brother, "Are-"
"DO IT NOW!" yells Gish.
Gash stabs open the bag of salt and as the salt pours into the crack in the ground, he enchants it into a two-headed snake. The senseless salt serpents separate and slither through the scar, spreading symmetrically around the circumference. As it flows, Gash screams a forceful wail at the worms still attempting to navigate the still-living (unliving?) wall, pushing them back off.
Gish stands and opens a portal back to the tower. The duo fling themselves back through and yell, "Circle's ready, Boss!"
L: I don't how they did it, but they ran like the clappers to get it done.