First of all, you need to press the 'ESC' button during the gameplay and just type 'GRIM' in the pause menu (not capital letters, you will hear sound for every letter of the word typed).

You will see a forgotten control panel, where you should tick 'perks in quests' (see below).
This is how Crimsonland was played originally, so I personally do not consider this a cheat. It will allow you to level up in quests and get some vital perks.

Okay, now it depends on the difficulty of your gameplay. If you are playing on Normal, it is generally easy to finish any level. What you need among your perks is just regeneration:
What you need is just having full HP at the end of the level - even if you took damage, you get a star if you complete the level at full health. Basically, that's it, and you can go and get those stars. Still there are a few tricks that help complete the levels, especially in chapter 3.



I also suggest getting Infernal Contract at normal difficulty if it is available:
You will be able to regen back from 1% HP (or restart if you fail to get one) but will also get up to three useful perks.




In case you got Infernal Contract, Greater Regeneration becomes an option:
It takes around 2-3 minutes to heal from 1% to 100% without greater regen, so if you're patient enough you don't need it :).

Okay, this build differs slightly from the general tips & tricks guide. That one works perfectly, but some aspects of Quest mode (no highscore needed, finite levels) allow an easier path to win.

1. You will need Mini-rocket swarmers. It does quite heavy damage compared to other weapons if you don't account for bonuses. The only drawback is that you fire the whole clip at once, and then wait around a second to reload. Why don't we improve that?

2.These are the perks you need:
Regression bullets - as you don't care about highscore, just don't release the fire button. With quite smaller delay between shots, Swarmers become a very effective weapon. Stationary reloader - you will have to keep standing to get almost same shooting speed, but most often you will be able to wipe most of the map.

3. The perks that could also help after you get that combo are:
Tough reloader - as you are constanly reloading, this will in fact make you two times more durable.
Fastloader - even faster shooting speed.
Ammo maniac/My favourite weapon - those increase the amount of rockets shot each time.
Angry reloader - makes you emit fireballs every 0.5 seconds, why not?

I also like to have Telekinesis and Bonus Economist regardless of the mode I'm playing.

4. If you didn't get the needed perk, go for Perk Expert, Perk Master, or Bloody Mess that would get you next perk sooner!

That could be more an advice for new players, as experienced ones are aware of that.
I will just post one picture that solves the problem (in addition to what's described above):






P.S. Doesn't work for normal difficulty level 2.10 - not enough XP for a level =( Try Gauss Shotgun, or HR Flamer. Also any Shotgun works if you manage to get 1 Fire Bullets or Shield (followed by Fire Bullets).

Good luck and go beat those aliens!