A quick note about these achievements: There are not enough enemy encounters in the game to max the 3 skill trees out in one playthrough. You'll have to start New Game+ afterwards to finish them off, unfortunately requiring playing through the first couple levels of the game again which offer basically no skill advancement. You can however skip most cutscenes by holding E on the keyboard, or some button (not sure which) on the controller. I was able to finish these achievements off halfway through Chapter 7 in NG+.

I hope these tips help anyone who's stuck or confused about how skill progress works in this game.

Skill progress is awarded after exiting each enemy encounter zone. How that progress is distributed seems to be determined primarily based on the manner in which you kill (or avoid) enemies during the encounter. I've seen some claims that the percentage of enemies you kill and how detected you were during the counter matter as well (IE less detection / fewer kills = Prudence, more detection / more kills = Aggressive, and Opportunism is in between,) but have not been able to confirm this.



Prudence progress is driven by stealthy play, though people have noticed that even when playing aggressively, Prudence still gains progress. I believe this is because any enemy you leave alive (possibly requiring they not detect you either) counts for Prudence. Killing enemies while entirely undetected may also improve Prudence. Either way, it's unlikely that most people need help improving this skill.



Aggressive progress is driven by aggressive play, or more specifically, direct kills. This includes:

• Killing enemies with the sling (direct rock to the head, or strangling them in melee)
  
• Killing enemies with the crossbow (regular bolts)
  
• Using Hugo's rat control power to kill enemies
  
• Killing enemies with a knife

If the enemies are fully aware of you when you kill them, all the better.



Opportunism progress is driven by indirect kills using alchemy making it a bit more complicated than the other two, so it's no surprise that far fewer people have this achievement. Kill methods include:

• Extinguishing a light source, resulting in an enemy being killed by rats
  
• Setting an enemy on fire with a pool of tar (Pot + Tar then throwing Ignifer if there isn't a pool)
  
• Setting an enemy on fire with burning tall grass (the stuff you hide in)
  
• Killing an enemy with rats using Odoris
  
• Knocking a fire grenade out of an enemy's hand, setting him on fire (later in the game.)

There are also two alchemy upgrades that unlock new ways to kill enemies and I have not confirmed whether these count though it seems likely: Throwing Ignifer at an enemy directly, and throwing Odoris into fire to create an explosion.