Monst3r's portrait

I've got something you might be interested in. I need a quick decision — this thing's hot.
—Monst3r

After the first mission, Central re-establishes contact with Monst3r, a freelance trader of items, weapons and augments whom Invisible has had prior dealings with.

On the world map screen between missions, the agency sometimes has the option to purchase something from Monst3r, for a 20% discount compared to their nominal value. Whether or not there is anything to buy from him, the agency also has the option to sell items, weapons or uninstalled augments to Monst3r, for half of their nominal value.

Monst3r has something for sale at some particular scripted times, and otherwise randomly. Any item, weapon or augment offered by Monst3r can be purchased only before entering the next mission; it will not still be available afterwards. Anything sold to Monst3r cannot be bought back from him. However, the same things may become randomly available to buy from Monst3r later.

Perhaps unexpectedly, trading with Monst3r outside of missions works no differently even when Monst3r is on your team as an agent, and even when Monst3r has been lost in the field; this is not remarked upon in the game.