Complete the game on any difficulty level

Complete the game on Extreme difficulty.

You need to find all the secrets in the second chapter.

Here's an excellent guide.
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You need to find stuffed toys on every level of the first and second episodes (excluding boss levels), as well as on the interlude, rd21demo levels. It is also important to reach the exit of the level while holding the toy in your hands.

Here is an excellent guide showing where to find plush toys in the first and second episodes.
Don't forget to thank the author with a like :)

At the end of The Train level, when you are given control of another character, you need to kill 15 cultists per minute with a sniper rifle.

Before exiting the level The Bunker, a boss appears. Defeat him, after which a second one will show up. Reduce one of them to low health (one shot away from death), then dodge their attacks while trying to maneuver the low-health boss into the other one's attack.

At The Train level, you simply need to push the cultist off the train.

At any level, you need to kill the cultist in the black robe before he lights the dynamite.

To obtain this achievement, locate a cultist armed with a grenade launcher. Approach him and kick him just before he explodes. If done correctly, he will survive and become your ally.

In the first level of New Grandewel, you will come across a bar. When you enter it, you will see a pool table with balls laid out on it. You will need to pocket all the balls. If you pocket the white ball, you will have to start over from the beginning.

In the chapter The Fairgrounds, as you progress through the chapter, you will come across a ship with three attractions next to it. We are interested in the shooting gallery (the other two are not necessary to complete, as you will not receive anything for them). You need to hit all the targets without missing a single shot. I recommend keeping your sights in the middle once the targets start to speed up. (there will be a teddy bear as the main prize right next to the shooting gallery).

The easiest achievement is located on the second floor of the. When you open the gate to the cinema (you will see a stand with toys; you can take any one you like, any will do), go through the upper right door, then turn left and go to the end, where you will see a red door on the right. Go inside, watch the credits roll, and just wait a while until you get the achievement.