Nuclear Titbit: Flashback

In the beginning, the protagonist finds himself in an enclosed building of six rooms. In the face of the protagonist is some kind of humanoid bald creature with an iron claw instead of one arm and a beastly smile. The rooms fit the creature's appearance - shabby walls with crumbling plaster in places, pentagrams with blood stains, crates of nuclear waste, mutant rats, and the biggest surprise - a man with an axe in his back, occupying the toilet.