Reclusive treasure

These appear to be a ring event. To start there are 4 linked 57s, as soon as these are slain you get three lined 57^. When those are killed, next pops four 57, which when slain give way to three more at 58. At any point along this chain if you don't kill fast enough the monsters despawn. I did not get a name at the end of the chain yet, but that may be because I am not killing fast enough solo.