So, you collect a bunch of prisms after battling in a vast open world, defeat three bosses in relatively sizeable arenas... ...then the final challenge is to fight several waves of enemies in a tiny square, which charges a teleporter...?
o_o I'm in the hopes that this is just a placeholder for something better. 
Firstly, charging the teleporter seems like a knock-off of Risk of Rain 2's teleporter events. It's not exactly original. It's just that time has been exchanged for killing enemies.
Secondly, is it a sensible test of a player's skills from the activities in rest of the cycle to just repeat these combat skills in a tiny space? It doesn't make sense. (Most of what gets tested are my camera skills, which is tiresome in a cramped space when using a controller since you have one thumb to either position the camera or use an action button. I dunno if anyone can do both at once.)
Here's a possible alternative way to end the cycles: 
-
The player is collecting both prisms and teleporter energy throughout the ***entire ***cycle from killing enemies. Maybe the elites have large globs of energy. Maybe the bosses drop teleporter energy in an amount that reflects how handily you dispatched them (by time or HP lost during the crown fights?)
-
The teleporter is always on the map, but can't be activated without beating the three bosses.
-
The teleporter is charged with the teleporter energy you collect during the cycle, gathered in labs, by defeating enemies, or from any number of methods in the large, open world. If you don't have enough energy after killing the three bosses, you have to make up for the rest when the Overgrowth goes crazy.
-
When the teleporter is activated, you then can either just use it, or you'd have to fight a single teleporter boss. Maybe this is where the assassins come in, since they just seem to get caught on terrain and glitch out right now. 🤪