Dark beasts are aggressive. If a player attacks them with melee, they'll attack with melee too, even if the player runs behind any obstacle/monster (out of the attack range of the beast) and comes back. If the player uses range/magic at long-range, dark beasts will attack with magic. Dark beasts use incredibly strong attacks, capable of hitting often on players using mid-high level gears. They are, however, weak to bolts, so using a crossbow of a decent level will be enough to kill them.