Shadow, are you able to give more detail on what the third card was yet?
I'm quite curious about that card as well (although I doubt Shadow will be allowed to spoil the card early). I just went through all the cards added in Warlord vs Forcemaster to try to pinpoint the other 2 cards he was talking about. I think one of them is Dancing Scimitar: it gives a free, relatively small attack every turn (perfect for depleting a forcefield). It also isn't mage or school specific, and doesn't even take up an equipment slot.
I still don't know what the second card could be. At first I thought it might be Battle Fury, but that wouldn't really speed things up since you'd have to give up an action to play it.
Double/Triple Strike and Battle Fury are... more complicated. In those cases, the second attack occurs within the first attack. The FAQ says that a token will be removed for each attack, so that's the black-letter rule, but I couldn't tell you why. Canceling the first attack should cancel all its steps, including step 5 (Doublestrike) and step 8 (Battle Fury). But the FAQ says to make those attacks anyway.
If I had to guess, that ruling is probably to keep the rules logically consistent without having to revise the attack sequence. It makes sense (especially to newer players) that having a hydra hit a forcefield three times would deplete it, so the rules bend to accommodate it. That is probably a good thing; I have seen a lot of reviewers compliment Mage Wars on its common-sense friendly set of rules.