Armchair expert here. What i would've done is: 1. Make the event harder, higher power level and extra modifiers. 2. Add an objective to reach the undying mind in the first place (maybe shoot semi-hidden oracles between each minotaur boss damage phase idk). 3. After killing the 1st boss, the portal can be entered to reach the undying mind area (I expected this from the Ikora portal). 4. Make the fight with the mind actually hard. It's the final assault for a reason. 5. Have it drop a weapon or gear! Perfect time for a new exotic imo (add it to xur's inventory later, so nobody misses out). 6. Done. Like i said, armchair expert. I know it isn't this easy, but come on.. all this build up for just a boss swap?