The Staff of the Leech is not meant to fulfill a role that I think needs filling in Dota 2, I just thought it was a cool idea for an item. The buildup is weird and bad but I tried for a while to think of a combination that made sense and came out to what I think the item should be worth (~2600-3000g). The active ability reduces an enemy's primary attribute by 15% and grants half of the lost attribute amount to the caster as the same attribute. This could be very useful against an out of control Undying or Centaur, for instance, if the caster is a hero that can benefit from a short burst of extra Strength. Likewise, if your hero can benefit from a short burst of Intelligence, casting it on a Skywrath could turn the tides, reducing his mana pool and the damage of his Q for a while. It can be used defensively to reduce enemies' damage or attacking capability, or offensively to bolster your own stats or reduce an enemy's armor or HP pool. The passive ability mostly just mitigates the effect of attribute reduction skills like Decay, but again only helps so much unless your hero can benefit from gaining the other two attributes. For instance, if you got Decayed by an enemy Undying with Aghanims, you would lose 10 strength and gain +2 to agility and intelligence for 20 seconds. Essence Shift is more confusing because you're losing 1 of each attribute per attack. The 1 strength lost would give 0.2 agility and intelligence, the 1 agility lost would give 0.2 strength and intelligence, and the 1 intelligence lost would give 0.2 strength and agility, for a total of 0.4 of each attribute gained per Essence Shift attack. This basically means that while Slark still receives 3 agility per attack, you are resistant to 40% of the attribute loss. To keep it slightly more balanced, each instance of attribute gain from the passive ability only lasts 20 seconds.