While on the Boss Mat, heroes must be standing on Hero Spaces to attack the Boss, where all attacks of any sort are considered in range. Certain spaces apply modifiers.
In the top example to the right, the hero suffers a -1 die to Skill Checks, and in the bottom the hero’s Agility roll is modified by +2.
When the Boss is in the Dungeon and not on the Boss Mat, heroes can attack it as if it were any other enemy. Roll a Skill Check comparing the Hero’s attack to the Boss’s (listed on its mat), but also note the Boss’s Counter-Attack.