Bill + Dipper = 💜💜💜

Demon Pony

The demon-pony hybrid bill cipher comes to bring nightmares to equestria but unicorn Dipper pines plans to stop him. Age adult and cutie mark is a blue pinetree.

Equestria

"Listen here your puny ponies!" An sadistic voice called out scaring everypony in Canterlot "If you don't surrender your land to me Bill Cipher you'll all perish!" He laughed evilly he was flying over Canterlot with his demon army behind him laughing as well he casted a spell to enhance his voice to Celestia heard him.

"What in the love of equestria do you think your doing!?" Celestia demanded her sister Luna behind her nodded not pleased.

"Well well well." Bill a yellow pony with blue eye that was flaming one had an eyepatch, a snake tongue, sharp teeth, horns, black and yellow mane and tail, Illuminati cutie mark, and a long sharp horn and dragon like wings "Isn't it my favorite alicorn sisters Princess Celestia and Princess Luna!" He said.

"I thought we locked you up long ago Cipher!" Luna said not wanting to play any games.

"Yeah and you really thought a 3 headed dog could keep me away?!" Bill laughed casting a spell on the sisters keeping them in a bubble watching them struggle makes him laugh he did the same to all the pony knights.

"Hey leave them alone or else!" Dipper shouted from the balcony of the castle horn flaring up.

"Ha!" Bill laughed hard and wiped an invisible tear "What could one pony do that Celestia or Luna couldn't!" His horned worked up blue ready to hit the mare.

"How about a deal?" Dipper asked her blue magic casting a treaty "You won't take over Equestria and I'll give you something in return! Deal?" She asked.

"Deal!" Bill went close to the mare making the tip of his horn touch hers sealing them in contract as their names names were signed in for the treaty.

"Dipper Pines what did you do?" Celestia asked flying toward Dipper Luna in tow.

"She just gave herself up!" Bill said a glowing blue chain is around his hoof and a collar is attached to Dipper's neck.

"I gave myself up - wait what!" Dipper screeched being levitated of the ground by Bill's magic toward him where he kissed her on the lips making her blush.

"Let's see how much fun you can be!" Bill chuckled and teleported away to his dimension long with his demon pals as well.

"I came as soon as I heard what I miss?" Twilight Sparkle said once she  teleported next to the two princesses who were left agape at what they just saw as well as their guards "I'm too late aren't I?" She asked ears down.