For every unit that could have defended, and did not, deal one damage. If i have malus darkblade, and my opponent is empire, has two resources, and ive played caught the scent and seen that he has forced march in his hand, can I deal 1 damage to any of his units in any zone? Because I guess he COULD defend if that unit was force marched into the zone im attacking.

I'm going to go out on a limb and say "no." Even if you replace Caught the Scent/Forced March with Pistoliers, I'd still say "no." Feel free to ask James if you want something official.

Oh yeah, I had one more question. One any of you could probably answer about Mallus. If i got a unit in a burning zone, and mallus attacks that zone, and i dont defend, because its pointless to defend, i still get dealt a damage? I though to defend, you had to be defending something.

in response to the first question, Could have is kind of a broad term. If they said Could have (barring card effects) then there would be no question at all.

All effects only ever count the cards in play so whatever they have in their hand is inconsequential. As to the Pistoliers they may have an ability that could make them able to defend if it was triggered at a certain time, but are not units which could be legally declared as defenders. Malus makes all units legally able to be declared as defenders in an attacked zone defend or take damage. The question in my head is about the High Elf quest Defend To Aendris. I would have to conclude that yes, they are legally capable of being declared so must or are subject to his ability.

i agree- units on that quest have the ability to defend any zone so they are certainly capable under a continuous effect, and all cards making that possible are in play.

Isn't Forced March "play during your turn"? If so, having FM in hand while opponent attacks on his turn doesn't help move defenders in anyways.