well, this is my 1st guide.
i cant realy guide about it, but it is a nice item combination.
at first it feels useless but in a game ezrael gets easy over 15 kills with 0 deaths.
the first question that will pop up is probably: why the F... use ocult and mejai,
well, that is becouse ezrael's spells use attack and ability power, so with stacking these 2 things with barely paying for it you create some nice damage.
with these items you will gain massive power over kills and assists.
this build is very nice when you are in the outer lanes becouse you will have assists to.
but i used it in middle lane to and it works like a charm.
i use my essence flux to kite the champions a bit, when they run away with a bit of HP hit them with mystic shot. i safe my ult for when they run away with a bit of HP to recall. just trow it in the deep and u'll get the kill.
this build is EASY to use vs the bots becouse they are easy to kite, when they run away to recall between towers. walk around and use mystic shot, its a garanteed kill.
use essence flux as much as you can on the champions and you will be ok.
when you have your stacks built up with mejai's and ocult you will take half their HP with your ult, which is very nice.
it is best to run out of combat then fight for the death, assists will still stack your attack and AP
ezrael is not good at jungling, she is more of a champion hunter.
i have bad runes myself and i use this build perfectly so take whatever you like.
hope you guys like it and vote for it ofcourse ;)

switch out:
rylai's crystal scepter for rod of ages. (mana and hp stacking)
guinsoo's rageblade for void staff. (against high resistant targets)
sorcerer shoes for ionian boots of lucidity. (cooldown reduction)
trinity force for rabadon's deathcap. (huge boost of magic damage)

Pros:
ezrael is a good kiter.
the ult is great for finishing far away targets.

Cons:
being ganked by multiple targets.
stun, which mostly follows up by a gank.
having a bad start, this will result in not stacking your assists and kills.