I see what you did there; you get a 9/9 Essence of the Wild. And a
.
You have two replacement effects here: Bloodthirst and Essence. Normally when applying multiple replacement effects you get to choose which to apply first, but there's a special rule (originally written specifically for Essence of the Wild!) that says that if you're applying multiple replacement effects and any of them cause an object to become a copy of something else, you need to apply that one first. So you apply the Essence's replacement first.
Now, if this was a normal bloodthirst creature like
Gorehorn Minotaurs, that'd be the end of the story, because turning the creature into a copy of the Essence would remove the bloodthirst ability, so there'd be no more effects to apply and you'd get a 6/6 Essence. But the reason this particular spell has bloodthirst is because the Bloodlord granted it to it, and that effect still exists and is applied to the spell, so you have a bloodthirsty Essence. Damage has been dealt to your opponent, so the replacement is applied and you end up with a 9/9 Essence.
Well, I was hoping to see mentions of Layers 1 and 6, but this explanation is good enough.
Thanks everybody who answered my questions. I knew the answers to each of them, I just wanted to see what the average response time was here.
And then decided to throw a sort of stumper out there at the end, which might have skewed things a bit.