I have played a lot of games with Abathur, this is the best damage dealing Build I have.

This guide works perfect with Illidan, Chen & ETC.

I know the talent tree can look very strange. I highly suggest that you take Evolve Monstrosity, the reason being, you want to use your Symbiote host in fights helping your teamates with attack speed, shields and also doing tons of damage with them. Taking Ultimate Evolution only gives away experience and does not provide much for your teamates, just because you can't ulty, I feel that you are a little useless compaired to if you had Symbiote host on your ally.

Please watch out for the treats listed, they counter you of some sort.

Stitches - If he eats the person your Symbiote host is on, your Symbiote host goes on cooldown and are removed from that hero.
Zerathul - His ulty also removes your Symbiote host from your target, but that is not the only problem, he also goes invisible, so you can not keep track of him, he could be looking for you without you even knowing it.
Nova - Exactly the same as Zerathul, she goes invis and could be looking for you behind your towers.
Zagara - She can also remove your Symbiote host on your ally and put it on a reset.

Please follow me on YouTube: https://www.youtube.com/user/MrMonzor1

Looking forward hearing from you!

Here are some footage how I play Abathur
Play Video