Quote from 2d-chrisThey might add some special units for the 2nd and 3rd game? But you can only use them in MP if you own them?
If you're refering to the "units will now be unique to the campaigns" comment, I imagine it's refering to stuff like the High Elves and Naga in Warcraft 3 - which only appear in the single player and don't really have any place in multiplayer.