Lets call it Singularity. It the ultimate of all ultimates. It requires lots of research and it consists of several if not dozens of elements from which you cook up your own personal Singularity. There are no recipes to buy. It takes weeks or even months to charge, depending of the resources it takes and damage it does, and when it launches it is a land wide phenomena like a dark anchor. It is a show stopper for all things it affects. It can be cast at enemies or friends alike. It can even stop the time for a while for everything around.
Say you make a Singularity you call Wrath of Heavens. It requires you to drink a certain potion, bring the time to halt and rise up to levitate 40 feet high above, walk through the air 20 steps, scream at the heavens as if you were dying and use your wand to draw in the power of all thunder clouds in the land to the designated point. The phenomena takes time and allows people to come see the show as it happens.
Engine-wise it could mostly combine the existing elements we already have in the game, added with something new. We've already seen some epic stuff in the dungeons and trials so I do not see technical obstacles. Biggest thing would be the system on how to build and research it, to make it complex enough so that no two Singularities would be the same. Hope this reaches someone out there.