I'm yet to lose a game since I started using this build I will give a brief run down on the how's and why's behind everything.

First leveling build -

Early game
The reason behind crimson slash is the nuke is at it's best early game. Your third skill is mainly to force opponents into bad positions and stop runners. 

Mid game 
By now you should have at least your lobo's and your Atlantean Seal which will give you a good amount of health to absorb blows. This is where you should see your third skill start to shine by making people beat on you while your team does the rest. Even with your skills on cd it should be nearly impossible for anyone to escape you with double slows.

Late game
This is where it becomes a little optional if you see you can take the enemy damage max your passive IT DECIMATES in group fights. If you're behind or you see that someone on the enemy team is fed level come at me for damage midigation.

Take note of how come at me's damage reduction works, I like to run into a pile of drones and pop it before I use overwhelming rage if the situation presents itself, If not wait till at least 50% hp before popping it depending on what the enemy team has, i.e. don't get bunnied and die without using it. Don't use your heal stolen power till AFTER you have used come at me.

Added tips Save come at me before an enemy uses their big combo or finisher, personal favorite come at me against green lantern's ult after it hits you for nothing they usually run for their lives and with your snares they aren't going anywhere.

Item choices - 
(Always buy Hawkman's Harness in between items, max it out and resell for full value and then buy your next item)

The only must have's for me are Lobo's chain and Atlantean Seal the double slows with the added health gives you a solid base against any enemy. (always my first two items after modded crime bible)

After you finish Lobo's and Seal assess the situation, see who the big threats on the enemy team are and fear accordingly examples.

If catwoman, gascat, ga or any of the like I like to go Fragment of Mogo as my third item to max, why? You want hp the more hp you have the more procs of your passive and the more health accounts for percentage for come at me midigation.

If sinestro gl shazaam or the life my third item will be Mirror Master's Prism to max, why? Same as above you want hp lot's of hp, believe me when your team realizes you have 3k hp they will try really hard to avoid you especially when you will keep them in place for your team to rip to shreds.

I will add amplifiers later as I'm still working on which is the best but I would suggest hp with attack armor and hp with power armor.

As for items I go with -
Overclocked The Crime Bible
Empowered Atlantean Royal Seal
Lobo's Chain w/ hook shot (may replace with Empowered Ra's al Ghul's Robe as noone can escape with the snares I put out)

Final note on items I prefer cosmic staff to starheart on Atrocitus his damage modifiers on skills are 35 and 40% on his q and e and his passive is 10%. That is too weak a percentage to justify going damage on him as where the staff will do a set percentage of damage over time and give you some cdr to go with your damage. 

I encourage every Atrocitus if you're going to pick a tank then TANK if you want to wtf gib someone with damage go green lantern or sinestro or any of the damage dealers. Believe me you can change a game with this hero simply by locking down the enemy glass cannon and watching him explode when you Rage on him.

Feel free to ask any questions or comment and I will respond.

GLHF and enjoy punting people with the red lantern.