What do you mean by tracking? O and I mean does it actually work against enemies? Or is it easy to see him
B q.u,1!
Tracking generally means he follows around one hero and kills them when they're alone, if that makes more sense?
He is 100% invisible when not attacking/using skills (items too maybe? as long as the enemy does not have true sight. True sight reveals all invisible heros, units, wards, etc. The other team can gain true sight in areas by buying items (sentry wards, dust of appearance, gem of true sight).
Sentry wards are placed on the ground and have a small area of true sight around them. The reveal Observer wards and invisible units.
Dust of appearance is used similar to a Healing Salve or a Clarity. One hero activates it from their inventory and it reveals all invisible units in an area around the hero who activated it.
A Gem of True Sight is held by one hero on the team, usually someone with an escape. It reveals all invisible units and wards in an area around the hero. It is dropped on the ground when the hero holding it is killed.
Enemy towers will also detect you when you are invisible near them and some heroes have skills that detect invisible heroes (Bounty Hunters Track, Slardars Amplify Damage) and AOE skills still work against you if you are invisible.