Complex sentence: Charlie, Marcia's boyfriend, disliked Archie because of his crush for Marcia, so he convinced the rest of the group to play a prank on him, which involved Charlie wearing the Horny mask and using a meat cleaver to scare him.
Split into simpler sentences: Charlie, Marcia's boyfriend, disliked Archie because of his crush for Marcia, so he convinced the rest of the group to play a prank on him. The prank involved Charlie wearing the Horny mask and using a meat cleaver to scare him.