To get this achievement you must first kill an NPC (I.e. with Leonora's pistol or knife) and then use Agnes' fly ability to dispose of the fresh corpse. Using the fly ability on an old, dissecated corpse doesn't count.

There's a hidden stat tracks your internal madness, I believe this goes up everytime your characters take sanity damage, or everytime they suffer a shock, so just keep losing sanity and checking the statue and this achievement will pop up.

You must use Alfredo's Sermon ability with at least 3 chickens in range.

You must cause a big ruckus, such as breaking a mirror so that nearby NPCs get startled. You can use Leonora or Eduardo and a wooden plank for this.

Interact with the statue of St Dymphna and advance time.