Complete the game.
Pretty obvious, just finish the story.
Collect 50% of the medals.
Private Eye 35 G
Collect all documents and objects.
Collect all the medals.
Use this guide to find all medals, objects and documents.
All can be found in one playthrough as long as you reload your checkpoint after using any bullets other than your energy rounds.
Complete the Challenge Room.
Once you complete the story you will unlock the challenge room. In this mode you have to fight off 5 waves of 10 enemies but you gain the power of Poseidon, allowing you to manipulate water.
This is quite easy and will take about 20 minutes. Make sure to complete it without firing a bullet to gain the two medals: Poseidon's Daughte
r and Hydro Power
Complete a hack.
Story related and cannot be missed.
Near the start of the game you will come to a hacking point, just match the signals and achievement unlocked.
Swept Off Their Feet 15G
Sweep 3 Malthusians off their feet with water.
You must use water to knock over 3 enemies. If you don't have this by the end of the game load act 2 and shoot the glass walls to bring water out knocking over the enemies. This can be done to the first 3 enemies.
Kill 5 Mathusians with fire or electricity.
This should come naturally as your progress through the game. Just shoot explosive barrels that you find on the floors and walls next to enemies or wires above them 5 times. Firing wires into the water that enemies are standing on will also electrocute them.
Chain Gang 15G
Kill 2 Malthusians within a timed chain attack.
Just simply kill 2 enemies with one combo. Pretty easy and should come naturally. There are plenty of times throughout the game where there will be 2 enemies next to a barrel.
My Hero 10G
Save Chief Billingham.
Near the end of act 1 you will have the chance to save the chief. When you use a control panel shortly after seeing the malthusians in person for the first time you will get a checkpoint and a timer will appear at the top of the screen. You must run back to where the police chief is, equip the Mavi whilst stood in front of the window and open the door behind him.
Davy Jones' Locker 15G
Neutralize 10 Malthusians in underwater combat.
You should be able to get this near the end of act 3 if not sooner.
Just use your energy round to knock out the malthusians underwater and they will eventually drown. Just do this as much as you can by flooding corridors and rooms then going underwater and you should be able to get this achievement quite easily.
Drown a Malthusian.
see Davy Jones' Locker