Thread:NoWayThisUsernameIsAlreadyOwnedBySomeone/@comment-26818419-20160801230502/@comment-26143371-20160802175719

Seems reasonable. I can think of the following ones:
 * Some of the stuff from the early events such as Christmas 2012 Event, Whacking Day 2013 Event and Valentine's Day 2013 Event. Most of those have been made permanent though in the moment the event was over, so I'm not sure whether all of them count.
 * Rewards from Insanity Mode and Rocket Launch Pad. I'd say those don't count since they require having a limited time item first.
 * Other stuff I've missed...