Looking for a dark psychological manga, similar to Prison Lab, preferrably. About an mc who is tempted by circumstances of impunity and desperately exploring a wide range of human desires and, of course, suffering of all the repercussions. With smallest cast of characters possible, just two - the player and the victim - is ideal.

Perhaps Liar Game

Tonari no Megane-kun has some harsh psychology in it, if you're ok with romance themes in it as well. Female lead is possessive, male lead wants her to cry for him and will use any sorts of methods to make her cry.
The male lead is mostly a Yandere 😃