For Flood Mode, all you need to do is open your conf.ini file and paste this inside:

[floodmode]

key=c5ca7a7e8bd8fe071ae8e587baa1a250436a62d5

.

Here's how to get it the authentic way (no conf.ini editing), it also gives you the achievements

1. Try to get a spawn next to wall, or in the corner (better option), you must be on normal or above

2. Get all 3 slush traps, and place a beacon as soon as you step into 1 (which is why I want you to have a spawn next to a wall or corner)

3. After getting all 3 slush traps, you then have to pick up the gun, NOTE: You must not pick up the gun beforehand.

4. Use your super weapon to kill the 3 little creatures that are colored yellow, they spawn where you activated the slush traps

5. After doing all of the above, finish the game like normal, hopefully you spawned next to a wall or in a corner.

Now enjoy Flood Mode!