Can you only attack each enemy once per round, or only attack each enemy once with each character? For example, if I have 3x mirkwood runners, could I have them attack seperately (rather than attack together) to trigger all 3 of their special abilities on the same enemy?

only once per player each round, so the runner cant all attack seperatly

rich

Actually, the limitation is each player can only "declare" an attack once against a particular enemy each turn; however, there is no limits on how many times a player can "participate" in attacks against that particular enemy (e.g. player A can join the attack declared by player B against enemy X through the ranged keyword, and player A can declare her own attack against that enemy X).