Undercake?
Sans was sleeping when he suddenly heard
"I'm turning twenty-something today" said Papyrus "but age is just a number so I am still young"
Sans doesn't care and sleeps again.
Then a reset happens.
The skeletons wake up and find a cake on the table.
"Your spaghetti sucks so have that cake" the card on the top of the cake said. It appears that Undyne snuck into their house and left a present.
Papyrus is mad so he looks for her.
"The Great Papyrus does a-great a-cooking!"
But she is already on the top of the hill just chilling. But her hair keeps getting into her mouth because of the wind.
So she cut all of her hairs.
"They look like a tomato-spaghetti" she wondered. "Wait it's Papyrus' birthday today!"
And she rushed to the skele-house and found the cake.
"Hey nice cayk" she said as if she was never introduced to it.
"Wait so if you didn't cook it, then who...?" Sans wondered
Then suddenly the top of the cake exploded and a human Flowey that was inside the cake appeared: "It's me bitches"
"Oh no an evil plan" said Sans
"I can finally stretch my legs" Flowey expressed his feelings.
then the cake ate everybody while everybody ate the Flowey.
"One day I will rule this world" said the cake
Notes: inspired by this drawing by the-trashlordDOTtumblrDOTcom/post/149393192446/idk-why-but-i-never-uploaded-this-before-what-a