The Mechromancer class DLC will be released on October 16, Gearbox revealed at their PAX Prime panel today. It will be free with pre-order, but $10 to those who do not.
Gearbox also dove into the Mechromancer's skill trees, distinguishing two contrasting modes: one that lets skilled players stack abilities in combination with her robot companion, and the other that helps less-skilled players with automated assists.
The Best Friends Forever skill tree—a "noobish-friendly" skill tree as described to me by Gearbox CEO Randy Pitchford—lets players who aren't great at first-person shooters be of some assistance in cooperative play. The BFF tree essentially sacrifices damage for aim assists. So a missed shot can reflect and hit an enemy 50% of the time. Deathtrap, the Mechromancer's robot, will be more automated, seeking out enemies to deal area of effect damage as well as status effect damage on enemies. On the BFF mode, Borderlands 2 handles the prioritizing of targets rather than asking you to do so.
But if you want to push the Mechromancer to her most dangerous form, you can invest in the Ordered Chaos tree that lets you stack abilities—using a skill called anarchy—for ultimate damage. This skill lets you calculate and plan hits based on your own strategizing. Stacking the Mechromancer's abilities can even involve imbuing Deathtrap with fire damage if you've got the right elemental weapon equipped and decide to include him in your stacked hits. You can invest in skill points in this tree to specify that a certain sequence of hits will give you bonus damage on a certain numbered hit. If you're airborn when you strike with a critical hit, the Mechromancer gets additional stacks of anarchy for more potential damage.
Gearbox was careful to mention that while the model of the Mechromancer herself is finished, they're still working on polishing her skills.