THIS IS DIFFERENT FROM MC-37586. I was playing on a LAN world with my cousin and I noticed there was a clone of my player, it had the same username etc., it also showed up in the player list. What makes this different from MC-37586 is that whenever I said something in the chat the duplicate player would say it also. Thank you in advance for reading this.
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Its still MC-37586. That something was said in the chat doesn't matter.