A new unit has been added: The Rogue. He can shoot enemies from a distance of up to 5 squares with the Shoot skill and the Ranged trait. However, this trait also has the drawback of causing the unit to deal only half damage with melee attacks. The Rogue also has the "Stealth" trait, which I'll go into more detail about below.
I have made major changes to the system which alerts enemies. Now, not only can enemies be alerted by seeing a hero, they can also be alerted if there is a suspicious sound. Moving a unit, attacking, using skills or casting spells will almost always generate some sort of sound with varying degrees of intensity. If a unit has the "Stealth" trait, the intensity of those sounds may be reduced or even eliminated, allowing that unit to move more freely without being detected.
Units with an Intelligence value of 2 or higher will call for help if they notice a sound, assuming that they are alive at that point. If a Rogue is strong enough, he might be able to kill an enemy instantly and prevent them from alerting other enemies to his presence.