Use it cautiously to avoid painful accidents. Where an Earth Tremor hits, rocks roll in and out of the ground, severely damaging anything in its area of effect. Earth Tremors are rare and should be used sparingly. In a multiplayer battle, it can be used effectively to trap or guard your back, as well as tearing your opponent to pieces. Darts are fast and rapid, but cause very little damage.
Charges are plentiful, throughout the game.
On harder difficulty levels, where ammo is limited, keeping your powerful amunition is very important. Using darts can help conserve your ammo from being consumed on weaker enemies. In a multiplayer game, you spawn with this weapon, in hand. With some good aim, it can do a surprizing amount of damage. You might even take a player down with it.