Prototype 2 isn't as hard as the first game in the series. Therefore this achievement isn't as hard as it looks or sounds.
This is because of the New Game+ feature that unlocks right after your first playthrough.
I would recommend starting a playthrough on Easy or Normal
and doing the collectibles and side missions in this playthrough.
While doing everything you will have level your character to about level 18 and a half.
After completing your first playthrough you will unlock the New Game+ option in the main menu and the Insane difficulty
(you don't need to select the Insane difficulty as the achievement also unlocks upon completion on Hard)
After that you will want to start a New Game+ on Hard
New Game+ just starts a new game, but carries over the progress of your character. Therefore you are very powerfull right from the start.
Just concentrate on the Main missions, don't bother with collectibles or side-missions this time. By the time you've completed 3 missions in the Red Zone, you will reach level 23 (and unlock the "All Growed Up" achievement)
Then there is the bossfight:
You will have to deplete his healthbar a total of 3 times.
The First round
In the first round the boss will be using the Blade, just keep avoiding him by jumping. The best attack to use against him are the Fist Power (the normal attacks work best of all, In between you could use the Hammerfist).
Note: If people are having trouble with dodging during the bossfight /during round 1, use Block instead of dodge. Somehow dodging wasn't working for me so I kept blocking the whole fight until he uses the Hammerfists. Block seems to work perfect versus the Blade and the Whipfist. Just time it like you do with Rockets. You can also constantly tap Block if you aren't so good at timing. That works 9/10 times. Personally I used the Tendrils instead of the Hammerfist. Tendrils seem to work too. Just auto attack 3 times after you block/dodge. Thank you "zero judgement" for pointing this out!
The Second round
The boss will be using his Whipfist. Everytime he attacks or is going to attack, just block him by using your shield. Directly after using your shield he will be stunned. Again the best attacks to drain his healthbar are the Fist Power attacks. When his health is depleted, he will be down. And you will have to go near him and press the X that apears above him.
The Third round
In the third round the boss will be using the power fist attacks. When he attacks he will jump. To avoid these attacks, just jump, so that you are behind him when he lands his attack. The best attacks to use here is the whipfist. (Jump + whipfist attack). Thanks GamerDtK78 for pointing this out.
I used the Blade instead, it's not that affective, but it did it's job.
At a certain point he will do a spike attack, just jump to the side to avoid those.
When his health is depleted yet again, press the X button prompted while near him. (For some reason I had to press the B button at this moment in the game)
A short scene will occur and a button sequence will start.
You will have to push the X-button en the RB-button when prompted. (this will attack the boss, and block his attack)
At the very end of the sequence you will have to press the Y-button repeatedly to consume.
(Note: When you die during the bossbattle, you will only restart current round. So when you die, you won't have to start all over again.)
A ending cutscene will play, and the endcredits will roll.
After the credits, the achievement will unlock.
In the end the second playthrough took me about 4-5 hours to complete.
PS: Some people say that you could also get the full 1000g after only 1.5 playthrough. This is when you start the first playthrough on Hard.
It is shorter, but a bit more difficult.
Now i can only say good luck, and have fun playing Protoype 2.
(When you vote negatively, please also put a comment why you voted that way. So I won't make the same mistakes in other solutions)