Congratulations, you are now ready to go to the final bossfight arena. Stand with all four on the blue symbol in the Kino projector room and you will be teleported to the arena.
You will now need to play a game of Simon Says (you know, that memory game). Go to the opposite side of the boss room and interact with the book on the pedestal, but before doing so it is advised to get familiar with this new area first. Be wary: zombies will spawn.
Once interacted with it, the book will open and browse through four pages, one at a time, showing an order of four Apothicon symbols. Remember this sequence of the symbols because you need to press these in the right order later on.
Now move to the other side of the room, the upstairs part, and wait for the symbols to appear one by one. The symbol will change every 3 seconds or so.
When the correct symbol for your sequence appears, interact with it. It will now turn yellow.
Wait again for the next correct symbol to appear and interact again. Repeat this until you have interacted with all four of the symbols in the sequence shown by the book.
After succeeding in this, a bright flash can be seen and a power-up will be dropped. Now, four phases matching with the Runes of Creation will commence: Fire, Darkness, Lightning and Light. Kill all Margwa's (and possibly other monsters) to proceed to the next phase. If this doesn't work, interact with the Book again after you killed all the Apothicons.
The Fire phase will ignite the arena in red flames. During this phase, the floor sets alight, lava appears and Furies and Fire Margwas will spawn. Stay away from the fire and lava, otherwise you might burn to death.
The Darkness phase will spawn Margwa's and rain electricity from above, buzzing around in the room. The electricity gives a little damage but don't worry too much about it. Try to avoid it, but keep in mind that electricity is less worse than a Margwa slash.
The Lightning phase will have walls appearing from the ground. Try to avoid them, because otherwise you'll die. Also try to avoid the ledges of the map, because sometimes you will glitch out of the map if you get too close to the ledge. Kill all Apothicons to proceed to the next phase.
The Light phase is the last one: Antigravity is activated and white round spotlights will shine in the room. You must stand within these spotlights, otherwise you'll get hurt.
Once you completed the fourth phase, the Summoning Key will fall down in the middle of the room. Pick it up and you will be teleported back to Kino der Toten, now carrying the Summoning Key.