Have a total of $100 million in cash. (Already spent money does not count.)

First of all: I know this "mission 1 fast money" tip is everywhere on the internet, well for consoles at least. With the PC version we have that new (I believe) difficulty setting: Nightmare, which makes the farming a bit easier as it grants huge money bonuses. And also I discovered a way to get through the level really quickly without stopping to hide behind the boxes. Not only saves time but also grants extra money.

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Alright, this is a little guide on how to make a million dollar in about 40 seconds of playtime. Very useful for achievement hunters to make fast money. It's all about positioning and a little bit of timing to get through the level very quickly, no fighting required.

Okay, to be honest, "40 seconds" is only the mission time. All loading times included (from mission select menu, playing through the level, back to mission select menu) it takes me 1 minute 30 seconds. But if you're fast you're getting $1,100.000. So that's an extra 100k.

As you will need to play this level quite a lot to get a hundred million dollar when starting from zero those extra 100k can save you some playthroughs and time. I was farming for 3 hours and made $70 million. I wasn't really focussed though as I was watching TV. And I highly recommend you do so, too (or some other side activity) as this farming can get tedious quickly.

In case you don't understand what's happening and/or don't have YouTube Annotations activated, head to the next secion.

Okay, if the video wasn't enough, here's what's going on.

Select Nightmare Difficulty (unlocks after some missions)
Select Mission 1: The Man Who Chose the Moon

To get a lot of money play through it very fast and without reflecting any bullets. So here's the video guide summarized in text form:

You can avoid most of his bullets (to get the extra money and AAA rank) by hiding behind the boxes to the left and to the right but this takes too long in my opinion as you also get more money (~$100k for 10 seconds) for being fast.
So instead of waiting just turn around for a split-second whenever he raises his arm to fire his gun at you. He will immediately stop firing. Or rather, he will not even start. With a bit of timing. Yep, that scumbag is an honorable guy, only shoots when you face him.

There are two or three spots where he shoots regardless of your positioning but in those cases he will aim at set spots so it's easily avoidable and you basically never have to stop moving.

Have fun farming... to get those costumes.. or other bonus stuff.