>_<

I got no combat augs at all, and that boss is unnecessarily fucking hard to beat.

Trying to melee him turned into an epic failure. The only tactic that sorta worked for me was circling around a pillar and shoot him with a pistol, but then he threw a bunch of grenades and I died.

how to beat ?

try again.  There's weapons in the room.

the minute you're dropped into gameplay, run towards the upwards right part of the room. There's a shotgun and grenades in there; that was essential to my killing him. Stun him with grenades and pump him full of lead, repeat.

He is standing next to a barrel at the start of the battle. Concussion grenades work against him. There is also ammo/weapons all over the place in that room.

Shoot, throw grenades, and run around.... that is all....
 It can be pretty tough , but the strategy is simple.

I didn't have any combat augmentations either, but I only died a couple times. Stay in cover, run away, stun him, shoot him, throw grenades and mines at him. Doesn't take too long.

empty one clip of machine gun rounds into him.he actually does not have very much life at all.
on normal I just hid behind cover and unloaded one clip on him. he died and I said "was that really it?"

I did him on hard, killed on third try. I had EMP nades since I expected that boss fight to happen. Stun him with those (think there's several in the room), shoot in head, repeat. A rocket launcher helps.

As soon as you start, shoot the red barrel next to him. The explosion will hurt him and stun him a bit. Basically, you want to get him near explosive barrels if possible (or use frag/EMP grenades) so that you can damage him and stun him. While he's recovering from an explosion, pump him full of lead. Just keep doing this pretty much. 
 
As for moving around, get in cover, wait for him to stop shooting, then sprint to more cover. If he gets too close, go in a circle around the cover until he stops shooting then make a run for a better spot. 
 
Bottom line: stay in cover, run in circles, 'splode him, SHOOT. 
 
ALSO: if you want to make future boss fights easier, get the augment that negates electricity damage (Dermal Armor) and the Typhoon aug. The Typhoon aug will come in handy for the 3rd boss IF you make a right choice at an earlier point in the game. I'll try to explain this without spoiling anything... You will be in the LIMB clinic in China and may be offered an unessential... thing. Refuse it, or the 3rd boss will be much more annoying. 
 
It's unfortunate the way the bosses were handled in this game. If you make different choices (story and upgrade choices) the bosses can become impossibly frustrating. That's a major design flaw.  
 
Instead of bosses there should've been more things like the that (second) time in China when 

I had a rocket launcher from the gang territory. I hit him with four rockets, one EMP grenade, and then a few pistol rounds to the head. I'm playing stealth and it was over in seconds. Easy.

What I did was this.
 
Stun gun, frag grenade, PEP Gun (I got that by breaking into the armory of the police station and that gun is awesome), stun gun, frag grenade, etc.
 
He ends up getting stuck in a loop that way.

I gave up on strategy on my 5th try and just ran around from pillar to pillar and took potshots at his head. Killed him in like 2 and a half clips.

I really liked the third boss. Like, a lot. For anyone who cares why, I've spoiler-tagged it.
 

Thanks for your tips , I will fucking destroy him and t-bag his corpse.

I unintentionally beat him by hiding behind a crate in the weapons room, he started to throw a shit load of greanades at me, but they bounced of the wall and killed him. It was quite funny.

I dropped a few things to get a rocket launcher a good bit before the boss. I saved it until then and just spammed rockets on him. It was so easy for me, and I didn't have any combat augs at that time either. 
 
Do you have any guns other than pistols?

A tip for all boss fights: if you have the invisibility augment, if you activate it, the bosses won't shoot you while you unload into their faces.

Took me a lot of tries but I ended up just chucking the poisonous gas canisters that are scattered about the room at him and shooting them to suffocate him in the cloud. If I remember right it only took about 3 hits to take him down on normal that way.

I did the terrible thing of preordering my PC version in Gamestop with a giftcard, killed him with Remote Explosives. Got the Typhoon after that, pretty much only use it on bosses (killed the second with two hits of it)

When you start out, turn around and go left(Or, turn right without turning around). There are going to be some barrels there. Pick up a red barrel and wait for him to stop shooting. Throw it at him. Pick up the second red barrel and do the same. Then go and find a yellow barrel. After that, hit him with the stun-gun a couple of times and boom: You've succeeded at defeating the first boss non-leathally.

The boss battles in this game are pretty bad though. After the second boss, I realized that just one guy came up with all of them and no one ever stopped to say "And then what happens?".

Don't need any augs to beat any of the bosses in this game :/

For the first one all it took was 3 EMP's and 3 rockets, dude was down without getting off a single shot.

What I did was this.  Stun gun, frag grenade, PEP Gun (I got that by breaking into the armory of the police station and that gun is awesome), stun gun, frag grenade, etc.  He ends up getting stuck in a loop that way.

I picked up a rocket launcher in the room with the mech-walker about 10 minutes before, so if it's possible for you to reload an earlier save around then, do it. 
 
I hit him with one grenade, and then two rockets before he even started walking (seems I got lucky, as he often began hunting me down as soon as I started aiming with the first rocket - took me 4 attempts because I kept scrolling and changing weapon when trying to get iron sights). Another rocket and a single revolver shot put him down. 
 
He is a fucking pain, though. Can't imagine how difficult that'd have been without rockets.

use stun grenades. its cheap but you'll get the job done.  

I was in a similar situation. I had put all my points into making hacking easier. In the end I had to turn the difficulty down. I only just killed that dude with about 4 or 5 hp left. Even then I used up all but 6 rounds for the 10mm and every grenade and mine I was able to salvage on my way to through the level.

Basically what I'm saying is if you ain't prepared, you need blind fucking luck.

If you have a stun gun, all you need to do is shoot him 15-17 times with that on hard mode. I know it's a cheap tactic (you can just stand in front of him and stun every time he snaps out of it to point his gun at you) but I feel the bosses are the major flaw in the game anyway so I have no problem being cheap with them.

At that time I didn't really have combat augs (personally I found no need). My weapon of choice was my twice damage upgraded armor-piercing pistol. EMPs (even stun guns) are very good for stunning to get a lot of shots in. When you see him throwing, just... Run? Take cover often? He dropped dead with 3 clips and three shots to the head, just to give an idea of how much health he has.

Did this earlier playing on normal, I had 1 point in the damage reduction aug and it was a walk in the park. Well ok I died once but all i did to beat him was stay in cover, blow up a couple of barrels, throw a grenade at him and unload a few bullets in him. It must of only taken about a minute or so to beat him.

Shoot head.

skip words too fucker

@SethPhotopoulos said:

What I did was this.  Stun gun, frag grenade, PEP Gun (I got that by breaking into the armory of the police station and that gun is awesome), stun gun, frag grenade, etc.  He ends up getting stuck in a loop that way.

You like the PEP gun?  I guess its a tad fun to play with... but I ended up selling it...  The one time I had fun with it was when I was blasting people off of roofs in China... Besides that, I'm a stun gun/tranq combo guy

Since it seems like you're going stealth, 10mm pistol with anti armor and grenades are your friends.

concussion grenades, stun gun and pistol.

@spankingaddict said:

Shoot, throw grenades, and run around.... that is all.... It can be pretty tough , but the strategy is simple.

This, it's how i beat him and i have 0 points into combat aug, shits a waste of points IMO.

The mines I picked up from the gang building served perfectly.  I'd sprint behind cover and as he slowly walked toward me I threw mines a few feet in front of him.  He was far too stupid to avoid them.

Throw barrels and gas canisters at him.

throw a (frag) grenade at his feet, then keep shooting his head when he's stunned. took maybe 5 or 6 shots and the battle was over in half a minute.

That fight was super easy for me. As soon as it started, I took cover threw three grenades at his feet and only had to shoot him a couple of times in the head with the pistol, done.

There's also a bunch of exploding barrels you can throw at him if I remember correctly. You should always move cover to cover or else he's just going to shoot you down.

First boss ended up shooting the exploding barrels around the room and killed himself. I barely did anything.

I ended up picking up the gas barrels hanging around, throwing them at him to stun him, and then picking up the exploding red barrels and tossing them at him. Took roughly 4 canisters total. Really easy.

Frag mines trivialize every boss fight in the game, even on "Give me Deus Ex" difficulty.

I beat the first boss by not doing anything at all. I couldn't figure out how to beat him and would just hide, when you hide he'll throw grenades out at random and they will inflict damage to himself. I was in the weapons room thinking about what i should do when eventually the "you killed the boss" cut scene came on.

...terrible terrible boss fights.

I had no problem with him. Shoot, stealth, run, throw a couple grenades. It wasnt too bad.

That second boss though, holy shit... I only managed to beat her because she somehow got stuck on a corner. Makes me feel dirty, but oh well.

I just emptied 1 1/2 combat rifle clips into his face.  The entire fight took under 15 seconds.

What I did was this.  Stun gun, frag grenade, PEP Gun (I got that by breaking into the armory of the police station and that gun is awesome), stun gun, frag grenade, etc.  He ends up getting stuck in a loop that way.

The only boss fight that I found difficult was that lady down in Picus. 
 
For the first boss, toss a few grenades in the beginning when he is still next to that red barrel and then empty a clip on the rifle at his head while hes stunned.  

For the 2 boss, I had difficulty with this but what I had to do was to keep running when your hp is low, dodge the 3 typhoon attacks for a counter and use cloak when things got too bad. 

For the 3 boss, the guy is a joke, if you keep circling around the outer lane, he’ll most probably not leave jumping back and forth the center divide. So you can just easily strafe him with a few shots of the grenade launcher and he’ll go down. 

For the last boss, its crazy easy. Assuming that you get the shutdown code from , you can just run to the center and input the code then run into the storage room that opens up on the bosses immediately left. You’ll have to clear the room of like 3 people though. Just crouch by the door way and empty a full clip with the laser rifle on her and its done. Less than 30 seconds.

Stun him (playing stealth, you should really have this [edit, by "this" I mean the stun gun), throw a red barrel at him, repeat. You may need a few rounds to finish him off.

Similar to others, without any combat-augs (pure stealth, pacificstic approach) - I took him down on the second attempt. My first attempt I attempted to do it "properly", but noticed that he became disabled for a significant amount of time every time i used the stungun on him.

On my second attempt, I just gave him a PEP-shot (mainly because I was worried about the range of the stun-gun), during the stun, I ran up to him, pulled out the stungun and proceeded to spam stungun shots in his face 'till he dropped. :)