"HMM... WELL, ALL RIGHT! I, THE GREAT PAPYRUS, WILL GLADLY COMMENCE WITH THE SWAPPING!" He'll go ahead and use his modifier skill to swap back to Chemist so that Frisk can do their whole stealing thing.

He's got his eyes on the Mimic, though. That clunking is a bit unsettling.

"COME TO THINK OF IT, PERHAPS TREASURE HUNTING WOULD BE USEFUL IN THIS MAZE, ANYWAY! GOOD THINKING, FRISK!"

But hmmm... what to do. Papyrus will go ahead and conjure up an Unstable Reaction for a bit of extra damage.