I just got it alone, without the second pad trick, with 2 lives left.
Here are my advices to take this big alien down :
- At the start : You can kill some soldiers in order to make weapons appear. Don't take the acid shot (green) because close range = danger during the first fight. The best you can pickup in my opinion are the orange or the purple ones. But keep in mind that your best friend for this fight will be the charged shot, so other weapons or grenades are just a bonus. Charged shots (or blast ?) (Hold X for a second) is the best weapon for this boss, helping you to stay concentrated on moving and dodging, plus it's way powerful and faster than several bullets.
- The first fight : This is the most complicated part. You have to be extremely careful to the boss' movements. Don't think about using your grenades, you should be as far as possible from him and attack with charged shots. A good way for this is to place yourself on the border and wait for him. If he comes fast to you, walking on the ground, you can jump over him and go for the other side. If he comes slowly, don't do it otherwise he will cut you in half.
Try to make him doing these comings and goings as most as possible. You can give him important damage during the process, little by little.
The charged shot is perfect as when you move, you charge your gun and you are ready to deal important damage.
While you're on the ground, go up if he jumps quickly towards you : he will certainly try to catch you. If he does, don't be scared, you may have your chance to survive : make sure he will punches you to the side where you have the most space and then try to dodge his attack. You have tour you jump/dodge as soon as you can.
When you're on a platform, NEVER stay if he moves quickly towards you : he's going to go down and cut you from below. Jump or dodge and go as far as possible to him.
Be ready to spot when he throws a smoking grenade : go up to not burn in flames. The best place to be is the far opposite from him or at least 2 platforms away. In order to get the more chances as possible, try the tactic said above to get him on the side, he might throw his special grenade when he's on the side of the screen.
When he shoots you while the floor is burning, attack him with charged shots and be careful to not maintain the DOWN button while you jump after crouching ! This will make you fall into the fire.
As soon as his life is almost down, he will attack more with his gun. This is the perfect moment to deal him a lot of damage.
During this round, you can lose 1 life, another one is ok but keep in mind that you need the maximum lives for the final fight. If you lose more than 2, give up already.
- The UFO : The first half of his lifebar is the easiest moment of this boss. You don't need to smash the X button forever, give your thumb a rest with using only charged shots ! If you have some grenades, save them for the second half of this round.
When he's going to fire his purple laser, stay in the middle and dig, you can be killed miserably if you don't.
The second part of this round starts when his life bar is half-down. He will launch grenades, so go up and use all your grenades on him.
Then, this is a very dangerous part, but you can make it without loosing any life. Attack only with charged shots while you're dodging the bullets by doing rolls. Try to stay as most as possible to the center and not to jump ! If you go to the side, you're more exposed to the danger and you may need to jump, which is more risky.
During all the fight against the UFO, you should not lose any life. When he takes you on board, you should have 4 or 3 lives left.
- The final fight : Again, stay to the side ! When he goes to you, jump over him, unload your charged shot on his head and go to the other side. If you can't reach him while he's shooting at you because of the ship's movements, just wait and dodge until he's within range. If he's within range while attacking you, this is the perfect moment to give him some blast shots !
When he will have half health left, helicopters will appear. You know what's going to happen to them so don't be underneath when they crash. He will destroy the one behind you and then go to the other side to do the same with the opposite one. Try to deal him the most damage as possible because it's going to be hard to survive then.
Now, this is the most difficult moment and that's why you need at least 2 lives left, as you are on a small platform in front of a guy who will cut you in half if you touch him ! To avoid this, jump over him only if he's going towards you and not when he's staying at the center in order to prevent to have him going to you when you land ... Again, blast him when you jump over him and when you're dodging his bullets. The best moments for you are when he's shooting at you from the far opposite.
He doesn't have many life left, so keep calm and stay concentrated !
This is the most difficult achievement to get in this awesome game but after a few tries, you will be able to do it !
(Please leave a comment if you found this guide helpful ;)