Luce? He's guessing she has a plan since she's running straight at Blanche but it's difficult not to jaw drop at her boldness or perhaps recklessness. Doctor grabs up his guitar again and strums away to build up energy again.

Successfully creating some sort of shield to keep Sans and Greg safe would be tricky- he stands a better chance of shielding Luce if Blanche strikes her. Whatever comes next, his best option appears to be to prep the spell and pray he has the power and timing to do the trick if it's needed. He watches, unblinking, for signs of Blanche's next move as he rushes to build up the magic energy.

Please let Luce's idea work.