Kill 30 enemies with Crossbow.

You will pick up the Helsing Crossbow at the start of the Taiga level as you approach a statue after being rescued from the water. The Crossbow is a silent weapon and is perfect for stealth activities.

Note that the achievement "Alyosha" and "Forest child" require that you do not kill the humans during the Taiga level, so to be sure you don't miss them, either make a save at the start of the level and then go and kill 30 enemies and then reload your save, or complete it in stealth and reload the chapter after having completed the game. You can still use the Crossbow after this level, but the enemies become fewer and less suited to be killed with a Crossbow than your other more powerful weapons.