Final answer:
The question relates to a fictional event in the Championship (MCC) Event 12, where no actual theft occurred. MCC is an entertainment event where and streamers play mini-games.
Step-by-step explanation:
The question "Who stole valuable items from everyone during MCC 12?" refers to an incident that occurred during the Championship (MCC) Event 12. The MCC is a popular online gaming event where and streamers compete in a variety of mini-games. However, there is no factual basis for in-game theft of valuable items as this is a fictional and scripted event designed for entertainment. If theft did occur, it would have been part of the scripted storyline for the event. It's important to recognize the difference between real-world events and those that occur within the context of a game or scripted entertainment.