Artist of War - 75G - Complete all campaign acts on Hardcore Difficulty
This speaks for itself really, go through all the chapters in the act to complete it then in the very last cutscene you will unlock the achievement, I would also reccomend doing it with a friend as that person can play the campaign on Casual and kill most of the enemies for you, this helps especially good for things like the Locust Fish as it is 10x easier for your friend to do it on Casual, If you do play it in Co-Op you should breeze through it, its not impossible to do it by yourself but some parts involving big enemies reavers, corpsers, even boomers can take too much ammo to kill by yourself, but if you do it buy yourself, every weapon try your very best to aim for the head, it takes less shots that way and preserves ammo, also use the chainsaw that solves a lot of ammo problems :).
If you havn't already completed the campaign on Casual, Normal or played the campaign with a friend you will get these achievements as well. I will list the 3 achievements below:
Campaign Difficulty Achievements:
Co-Op Achievement:
You will also unlock various other achievements along the way for Co-Op, story progression, killing enemies with certain weapons and also you will unlock 'Insane Difficulty' for doing this but if you havn't finished the game at all, you cannot complete it on the hardest difficulty the first time around, This should be pointed out.