Those of you who have entered a shadow lair should know about a the swarm. If not, there is a wiki page about it.
My suggestion would be, To have items that can only be crafted from 5* items that are "Swarm Infected" items. For example, there are snarbolax coats but there isn't a Rabid Snarbolax coat. It takes a Snarbolax coat, a vog cub coat and various materials to make, and it would be an green Snarbolax coat with a dark aura seeping from it and gives a lot of shadow defense, a lot of elemental defense and some normal defense?
There could be a Romulus Suit Swarm Suit made from Mercurial Demo Suit and Heavenly Iron Suit and so on.
I'm not going to list all the possibilities but these would be really powerful armors and should only be rewarded to those who have beaten shadow lairs.
I don't know if the core is being worked on or if it will open and there will be missions in it, but these armor sets could be rewarded only to those who have beaten it and collected Void shards or something that can only be collected from the core or possibly shadow lairs.
"Make really OP items!"
No.. just.. no.