The second day of Mann vs Machine details have rolled out, discussing some of the more strategic elements of TF2's freshly revealed co-op, PvE horde-mode. Upgrades! Currencies! Potion type canteen things! Tactics! A hidden, clickable grenade launcher even reveals the UI you'll be using to embolden your armoury between waves. It looks nice! And it all arrives tomorrow!
The flesh-on-metal Mann vs Machine mode will employ an upgrade system that allows for an improbably broad range of different, intermingling co-op capabilities. The post gives some examples of how these skills might all work together, as well as how players will evolve as the game progresses. The Pyro, f'rinstance, can upgrade his airblast to push bomb-carrying robots in mineshafts. A suitably upgraded Engineer can build a second mini-sentry, or use a Critical Hit canteen to boost a sentry gun to three times its firing speed. The Spy can upgrade his sapper to turn it into an area-of-effect robo-disabler.
Mann vs Machine isn't just a new game-mode, it's a new game. It has more in common with some other thing that's not TF2, maybe a MOBA of some sort - clearly Valve's work with Dota has brushed off here.
Tomorrow (or later tonight), we learn about 'Bounty', which I suspect has something to do with the scores of individual co-op players and how that might effect the amount of robo-aggro you attract. And then? Then it's out, the robots arrive and we take to arms.