League of Legends (LoL) Question: Essence Reaver On Graves?!

If you can manage your mana and buy a mana potion every once in a while you can buy more potent items. You stop being manahungry late game.

It gives 10% CDR, 10% LS, 80 AD & mana on hit. Your abilities do not apply on-hit effects and therefore you do not gain mana by using your skills.

I feel the stats are kind of random tbh, you get the most out of him by buying standard ADC items. (It's viable, but not the best choice.)

I also advice against building him tanky. You scale with AD, not armor or health. Your DPS is highest going glass cannon (your passive protects you btw) with one defensive item, if needed.

Learn to kite & orbwalk and you'll be doing fine.

For Graves I recommend you the standard ADC build.

2 Doran's Blade > Infinity Edge > Berserker's Greaves > Phantom Dancer > Last Whisper > Bloodthirster > Blade of the Ruined King/Mercurial Scimitar/Banshee's Veil. The last items are depending on the situation.