Shadow Warrior

All the power, skill, and weapon upgrades appear to require a second playthrough. This is not correct.

What you want to do is save up a specific amount as follows:

Weapons: $5000
Skills: 3 Points
Powers: 3 Points

Now, if you look at the achievement meter, buying a new upgrade will increase that respective achievement. If you save before doing so, and reload to buy it again, the achievement doesn't give further progression (for every other achievement in the game, it does).

However, if you buy an upgrade and reload, you can buy a different upgrade and gain progress for it as well.

So, you can get this achievement as long as you reload and buy every skill at some point. The game won't check to make sure you have them all right now. At the end of the game, I didn't have enough. I just loaded an old save where I had a lot of everything saved up, bought new stuff, reloaded, bought more, etc. until I had the achievement completed. Easy!

This should save you a huge amount of time playing through 1/3 of the game again.

To get power upgrades you have to collect chi crystals. In most missions you will find 1 chi crystal and they are hard to miss as they are on your way when progressing through the levels.

So after 1 playthrough you will still miss 6 upgrades. To get these you have to start a new game using ex mode which is basically a new game+ (you start with all your upgrades, weapons, cash). I got the achievement in chapter 5 (there are 2 chi crystals in that mission).