Slark is a "hit and disappear" hero that needs not too much farm to become a deadly carry even in the earlyer stages of the match. Slark can rely both on skill damage and immobilization early to get many early kills and on the essence shift as his ultimate ability for carrying the team .The way you should fight is hit hard and be aggressive and when you are wounded get back and whait for Shadow Dance to put you back on the first line. To maximize this get both health and agility.