Phantom Assassin

Tips

 * Stifling Dagger has multiple uses. Early in game it should be taken fast, as it allows you to last hit creeps even if they are far from you and later on allows you to slow enemies at a great range. Avoid using it as a harrass tool in the laning phase, as you'll be losing a good amount of CS and it won't deal enough damage to ward off your enemy. You should use it on enemy heroes when the enemy backs up and use items such as Clarity and Healing Salve to break their effects.
 * Phantom Strike can target allies and enemies. Jumping to a friendly unit can be useful in case Mortred needs to escape