Join
Joining is a feature where a stack of wandering creatures are willing to become a part of hero's army for free or in exchange for gold. Whether or not the stack will join depends on several factors, but basically if hero's charisma value (C) is lower than creature stack's mood value (M) the creatures will fight.
M > C → Creature stack will fight
M ≤ C → Creature may join
C = P + D + S