Kevin B. Smith
A) On Monster cards: What is [the speed value] for?
The rules imply that some monsters might be able to use speed as their attack. I don't know if any of them actually do.
B) On Hero cards: why is it counter-attack diamond icon?
I had never noticed that. I think the answer is found on the reference cards (that says "Symbols" at the top): The circle (attack) means "may initiate attack", whereas the diamond means "may not initiate attack". Since speed appears alongside melee and magic, if it were in a circle, people might think they could use it to attack monsters.