Before the knife could reach Sans, a skeletal hand with a hole in the middle of it blocked the knife. Frisk looked up and was met with a skeleton, covered in shadows and smoke as it stared down at her.
???: You
Frisk: It can't be. Your dead.
???: No anymore
Frisk backed away, fear in her eyes. The shadow skeleton then pulled out a file from his body and opened his mouth, releasing a high pitch computer squeal.
A wall of fire balls then charged to Frisk. Frisk rolled out of there way, but was hit in the face by a bone, knocking her to the ground. She was then forced into the air by a spider that pushed her into the air and into the path way of a bunch of spears, but strangely enough, the spears didn't damage Frisk's body, rather Chara's soul. Frisk was then pinned to the cave wall, allowing for a broken looking Gaster Blaster to aim at her, charging up it's black colored laser. Frisk quickly ripped the spears out of Chara's soul and they fell to the ground, dodging the laser. Frisk stood up, only for the shadow skeleton to grab her by the throat, plunge his ghostly hand into her chest, and pulled out Chara's ghost out of Frisk.
Chara looked up to the Shadow Skeleton in fear
Chara: Gaster!? How!?
Gaster: You won't live long enough to find out.
Chara: Yes I will.
Chara, also being a ghost like Gaster technicality was, was able to hurt him without a host. Because of this, she stabbed his chest and he dropped her. Allowing her to fly into the nearest wall and vanish.
Gaster grunted in pain, but soon picked up Frisk's unconscious body and brought her over to Monster Kid and Sans.
Monster Kid: Um...stranger, thanks?
Gaster: It is an honor, Monster Kid.
Monster Kid: How do you know my name?
Sans: That doesn't matter. Let go of my daughter in law.
Sans said to Gaster with anger in his eyes. Gaster sighed in defeat and looked to the ground sadly. He then gently placed Frisk on the ground. Sans then held Frisk in his arms.
Sans: Frisk, wake up...
Sans pissed expression turned into that of a sad one. Monster Kid nuzzled Frisk's head, as they tried to wake her up, but she wouldn't. Sans thwn reached to check her pulse.