Okay. I'm playing with my friend on his hosted world. We just started new characters and a new world yesterday. Today, we fought the brain of Cthulhu and beat him. We then decided to try a second time, and broke all the hearts needed to summon him. This time, when we broke the last one, we got the message "creeper has awoken" and nothing happened. After about 3 minutes of milling about searching the crimson caverns, we started to see un-killable creepers flashing around us with no brain to be seen anywhere. Has ANYONE experienced anything like this? I would like to state that this is completely vanilla, current version.