"Sans and I were having a friendly match. Undyne and Papyrus were inside caring for Alphys. Gaster was salvaging the remains of Sans's lab. So what went wrong? Why did Sans collapse?" Ammy thought to herself, sitting on the roof. Suddenly, the roof panel opened up to her left. Gaster climbed up the ladder and sat on the roof next to Ammy. "Any news?" she said, searching his face for any sign of emotion.
"Good news? Sans is awake. He simply fainted." Gaster replied.
"Good. Anything else?"
"Well, do you want the long explanation, or the paraphrasing?"
"Lay it down for me. I want all the info."
"Okay then. When Sans was unconscious, he was just laying there, right? Well, I was sitting there for a while when his eyes opened. He was using magic in his sleep! A dozen gaster blasters appeared behind him. I backed up. But then Sans started to shake. I knew he was going to change into his true form if I didn't do anything about it, so I talked to him. The gaster blasters disappeared. I stopped when his eyes were glowing green. I left the room, confident that he'd be fine. About 15 minutes later, he woke up. And that's all that happened." Gaster said, contented.
Suddenly, the panel opened again. Sans climbed up, holding a cup of coffee. Ammy saw that the coffee was made of healing magic. "Are you okay, Sans? What happened?"
"I'm fine, I just- woah-kay." Sans said, teetering. Gaster reached out to support him. "Sorry, I just… wait. Ammy, how much do you know?" Sans said, curiously.
"Just lay it down for me. If I ask, you just have to answer. So go ahead." she replied.
"Okay, so I was fighting, and something snapped. I guess I was reaching the threshold. I felt it stack, and….snap. Just like that, I fell." Sans replied, snapping for emphasis.
"So why is there a threshold?" Ammy asked.
"Basically, all skeletons have a 'true form' that they have to use sometimes. Mine is a dragon. And Gaster…" he replied, eyeing Gaster.
"I'm your father." Gaster replied, "of course I passed it down to you. But Papyrus's came from your mother. His is an eagle."
"I knew Papyrus's is."
"Sans, who was your mother?" Ammy asked curiously.
"My mother's name was Hermann. She died." Sans answered, his mood immediately darkening.
"I'm sorry for your loss." Ammy said, her voice wavering.
Sans took a drink from his cup, looked out to the distance, and teleported. Gaster, looking frustrated, teleported after him.
The empty cup fell to the shingles and shattered.