The other planets under Sol's domination had been visited, or at least probed, and to some extent were being colonized and exploited--but on the whole they had proved disappointing. No life to speak of. No intelligent residuum.
-Emil Petaja: The Nets of Space (1969)
To take this phrase out of context, here's an idea for 4e: INTELLIGENT RESIDUUM. When you melt down an intelligent weapon, you get this stuff. If it's used to make a new magic item, that item gets the former weapon's personality.
In powder form, the residuum still possesses intelligence. It can travel on its own, like a vampire in vapor form, and try to possess people for short periods (either to communicate telepathically or to dominate the possessed creature: it's a Will attack to possess a creature, and a save ends the possession.) The vapor is immune to melee and ranged attacks, but bursts and blasts automatically kill it.
The residuum can, over time, exert enough force to pop the cork on an ordinary residuum vial, but any stronger form of containment will trap it.
What does intelligent residuum want? Well, it depends greatly on personality, but probably to be used in the creation of a powerful item.
More in everybook