Undertale meets Shield

Planning

"Glitchtale." Justice said, Gaster looked at him with the blank but creepy expression. "He doesn't deserve this." He said, Gaster narrowed his sockets. "He's been working with the people that hurt my sons. How does he not deserve this?" Gaster asked, Tony tried to get Gaster hands off him as Patience got an idea. She stood up and clapped her hands together, blue sparkly dust came off her hands and landed on the ground.

"Would Sans want this?" She asked, the avengers looked at her as Kindness tried to heal Chara. The dust then became a swirling tornado and finally took the form of a happy, smiling, blue jacket Sans. Gaster let go of Tony who gasped and watched as Gaster walked over to the hologram of his son. "Would he want you to hurt people that-" She gasped when Gaster swung his hand through the fake version of Sans. "Don't mock me for your powers, child." Gaster said and glared at Patience who trembled in fear. "I am simply doing exactly what Sans did when they," He pointed at Frisk. " killed Papyrus themselves." He answered, Patience lowered her head as the avengers looked at Frisk in shock. Gaster then gasped as grabbed his chest and leaned against the wall as he began to glitch.

"W.D Gaster?" Perseverance asked as he stood up, the glitching stopped to reveal the original Gaster. He took a deep breath, stood up and looked at his hand to see it was melting a little. "We must hurry, the bridge between worlds is burning." Gaster said and turned to face the Avengers with a blunt look as his hands were behind his back in a respectful manner. He looked at Frisk and narrowed his eyes slightly before looking up at the Avengers again. "I know you do not trust, nor have I given you a good reason to." Gaster said as he walked closer to the Avengers but stopped and saw the state Chara was in. He raised a hand and a giant version of his hand went above Chara, the circle in the hand glowed green. "But there is a great evil amongst your people." Gaster said and faced the avengers.

"Who is it?" Nat asked, Gaster chuckled. "This monster is far from feeling anything human like." Gaster said, while on the helicarrier, Fury was sleeping on his desk, papers, pens and tablets littered it as he snorted. "This being is filled with the one thing humans are made of and react to." Gaster said as two pink dots appeared in the shadows. It chuckled as it saw him. " It has already killed so many people in its original home and it only has one purpose." Gaster said, the being then stepped out of the shadows to reveal Betty Noire from Glitchtale holding her scythe in hand. "What exactly is it supposed to do?" Steve asked, Gaster sighed and looked at the blue dust that was still on the ground.

"To make sure humans and monsters never get along. No matter what." He said, the avengers eyes widened at this. "No magic or weapon can kill it, for it is not a human more monster." He said, Betty walked over to Fury and chuckled to herself. "You sure have been doing a good job doing all my dirty work. Why not take it up a little." She said and snapped her fingers, she chuckled as she gave him a nightmare and disappeared into the shadows before he woke. "Then how do we stop something that can not be killed?" Thor asked, Gaster looked up at the wall.

"The void, I am aware I've broken it but I do believe there's another way to fix it without sending me into it." Gaster said and looked at the avengers. "I just need the original human souls of my world, however..." Gaster said and looked at Frisk who began to glitch. "Me glitching will only get in the way." Frisk said, Gaster nodded and looked up at the avengers. "If you leave the child with me, you can go back to your work and find the one who caused this whole mess. I have enough magic to summon Ink Sans, Error Sans and CORE!Frisk here to help make sure we can patch it up together." He said and sighed when the avengers hadn't moved.

"Why should we trust a man who hurt his own sons?" Banner asked, Gaster gripped his hands and sighed. "It was not my intention to hurt them the way I did. I was only a child when I saw almost all of my friends brutally murdered before my own eyes." Gaster said and glared at Tony. "So really, it should really be me who second guessed why I should even put my faith in you heartless beings." He said, Tony stopped for a second and looked at the human souls surrounding Chara as they were being healed. "At least you all were sparred with not seeing how your fathers died." He said and turned around from them. "But what would I know about love, I'm simply just stretching my neck for an entire civilization that I don't know." He said and turned his head slightly to them. "That surely should sound familiar to at least some of you." He said, Frisk got up and walked over to Nat.

"Sans still might be angry with me, but it's also my choice whether or not I use my soul to save thousands of monsters." They said, Nat looked at the group of human souls again and crouched down to Frisk level. "Are you sure?" Nat asked, Frisk gave her a thumbs up while glitching a little. "Trust me, I sometimes tag along with Sans on his trips to meet his alternate versions of himself." Frisk said, Nat smirked and stood up and nodded to Gaster. "Great, I will simply teleport Frisk to you all once we've fixed the void and that should take Betty Noire back to their home. Bye now." He said and flicked his wrist, teleporting the avengers back to the quinjet on the surface.