Very easy achievement. From the main menu, highlight ‘options’ and input:
,
,
,
. This brings up the cheat menu. Enable all the cheats to make this much easier. Set the start area as the HQ.
The pools of acid that some enemies create can still damage you so keep that in mind and avoid these
,
,
,
. This brings up another menu, select backer 7 ‘Jacqui’ and area as the HQ
Then start the game and finish the level, very easy and you can also go in each available room, going left/ right before up when you have the option and get all hostages for
And
You should also get another achievement for finishing the game with the good ending
Then feel free to repeat on Easy for