I got an Osprix (that revives after two seconds) as the final monster to kill in a Monolith of Fate run. After I killed him the window came up to open the portal. Then the Osprix revived and started attacking. I guess I wasn’t done after all. It seems if the Osprix is going to be a final monster to kill then the run should not end until the Osprix is really, really dead.
I had to contend with the Osprix, the portal to open and all the loot that dropped. This easily could have ended badly.