By the way, for people who think that mercs are unbeatable and cheesy, spy aggro isn't dead. Check out the Aqua video on
this thread.
Now, of course, Deathmatch games tend to get rather silly, because all a merc has to do most of the time is sit in a corner and camp like mad. No visible back, no neck-snapping. No place to jump on him from, no jump kills. Unfortunate, but true. However, mission aggro is still very much possible, because the mercs need to stay mobile in order to keep the objectives safe. They can't just sit in a corner and expect to win.
As for online training, tutorial mode is in the game, but sadly, it's not 2v0, but rather lets both teams talk to each other over voice communication. That's actually pretty good if you're training a buddy to be a spy, letting him know when you're suspicious of his position, or when you hear him, etc.