"ugh... that being said... you uh, really like swinging that thing around huh?"
"..."
"listen. i know you didn't answer me before, but... somewhere in there. i can feel it. there's a glimmer of a good person inside of you. the memory of someone who once wanted to do the right thing. someone who, in a another time, might have even been... a friend?"
He looks desperate. You feel strange. You feel... sad? You're losing control. Frisk is breaking free. They're trying as hard as possible to break out. You can't keep them in; they take over. They reach towards Sans.
"c'mon buddy. do you remember me? please, if you're listening... let's forget about all this okay? just lay down your weapon, and... well, my job will be a lot easier..."
They press the mercy button.
"i knew you were in there buddy. c'mon. let's hug it out."
They approach him and try to hug him. You quickly regain control and dodge the bones sprouting from the floor and try and hit the trickster whilst he's vulnerable. He dodges.
"welp, it was worth a shot. guess you like doing things the hard way, huh?"
It was a trap. He knew that Frisk wasn't the one doing this. He just wanted to find an easy way to secure your death. This battle was far from over.