So this story came to me when I read GearSolidSnake's review on the first chapter of my What Went Wrong story asking about the prank, so here it is, part one of The Prank...

It was another normal Saturday afternoon; Mordecai and Rigby were raking the leaves as usual. When they finished raking them Mordecai turned to his friend and asked, "Hey Rigby, can you grab the rubbish bags and start putting the leaves in"? Rigby nodded and went back to the shed, when he came back Mordecai was gone and there was a note saying: 'Hey Rigby, I'm going to get the game console running, be back soon'. Rigby just groaned and walked over to the leaves. As soon as he approached the leaves the pile practically exploded. Even over the rushing sound of the leaves in his face Rigby could hear a leaf blower. When the leaves blew away Rigby could finally see Muscleman with a leaf blower and a smile on his face. Muscleman chuckled and shouted, "Got ya dude"! Rigby then ran off to the house shouting, "Gross! I got it in my mouth"!

As Rigby reached the front door of the house, the door opened to reveal Mordecai standing there. He had a surprised look on his face and asked, "Oh Rigby, you finished already"? He then shook his head in reply and grabbed Mordecai's hand, leading him up to their room. When they reached it, Rigby locked the door and turned to Mordecai. He took a deep breath and then said, "We got to do something about Muscleman". Mordecai sighed, "Let me guess: another prank"? Rigby nodded and they then reflected on their "friends'" pranks:

Flashback:

Monday:

Mordecai woke up in the morning and decided to get out of bed, but as he swung his feet out he knew something wasn't right. He then decided to open his eyes and realised that his bed was floating down the river. He looked around to see Muscleman's' car driving next to the river, then the green man opened the window and shouted, "Got ya dude"! Mordecai then fell out of bed and into the river…

Tuesday:

Rigby walked back inside the house and saw a large chocolate cake on the kitchen table. His eyes lit up and he immediately rushed in and grabbed a knife and fork, ready to eat the whole thing and blame it on someone else. As soon as the knife hit the cake it popped and Rigby realised it was a balloon and cardboard. It had covered him in flour and Muscleman walked in laughing like there was no tomorrow. He then shouted, "Got ya dude"! Then Rigby realised that he was covered in itching powder and not flour…

Wednesday:

Mordecai was bushing his teeth after a long day of work when all of a sudden Muscleman came in shouting, "Got ya dude"! Mordecai was about to take out his toothbrush when he realised he couldn't. As Muscleman starts laughing harder Mordecai grabbed the toothpaste tube and pulled of the fake label, realizing it was dental glue. He ran to Rigby saying, "MMNY, MLL NM MMBLNE"! Rigby gave him a confused look asking, "What"?

Thursday:

Mordecai and Rigby were walking up the stairs to their room when the floorboards beneath Rigby collapsed and he fell through. Mordecai shouted, "Rigby, are you all right"! Muscleman appeared at the top of the stairs and shouted, "Got ya dude"! They then looked back to the hole as Rigby screamed, "AH! I LANDED IN A BOX FULL OF PINS AND MOUSE TRAPS"! Then the snapping started before Rigby shouted, "LOADED TRAPS"!

Friday:

Mordecai and Rigby woke up to complete darkness, Rigby then asked, "Hey Mordecai, can you turn on the light"? He did as asked and they both started to scream as they saw zombies surrounding them. They reached in to their draws and pulled out a pair of revolvers and started firing until they ran out of shots. They realised the zombies were actually manikins dressed like zombies. Muscle man walked in, wearing full body armour, and shouted, "Got ya dudes"! The police later came over and confiscated their zombie survival kit guns after the incident…

Present:

They groaned and then started to pace the room, trying to think of a way to get Muscleman back. After about five minutes Mordecai stopped pacing and snapped his fingers before saying, "Dude, Rigby! I have a great idea". They then huddled together as he explained the plan, planting grins on both their faces…