VG Item: Eve of Harvest

this crystal is use to build path his strong abilities is good

All of them.

Basically, if it's an ability or from a blue item, then stuff involving crystals and shields affect it. If it's an autoattack or from a red item, stuff involving weapon power and armor affects it.

Yeah alternating current damage and base damage of abilities? Or only crystal power

Do you get life steel from the crystal damage of basic attacks when used with alternative current?

Might have to play around with this in practice mode!

The lifesteal should be worth about 1000g to you, otherwise it's a waste.

For the lifesteal to be more effective than just plain health in a teamfight, you would need to deal more than 3,000 crystal damage while you are hurt.

That's a little bit unrealistic though, because
A) chances are you will be dealing crystal damage to non-players between fights and heal to full health
B) more health means the enemy can lifesteal more from you
C) more health means you get more hurt from %hp damage, etc.

The cost of the lifesteal is also the same as the cost of the physical lifesteal on serpent mask.

However, because skills can be used quickly, most crystal damage is dealt at the start of a fight, so be sure that you will be dealing crystal damage after you get hurt, otherwise this item is wasted.

It looks like the developers knew this, because they gave this item 25% lifesteal while serpent mask has only 20%.

You can check out my guide that uses two EoH and 2 Fountain of Renewals: http://www.vaingloryfire.com/vainglory/guide/a-modest-catherine-433

You'll never run out of health.

good idea to build Catherine with copies of this Item?
I once tried with 2 EoH (Eyes of Harvest) but the life-steal wasnt change significantly