Beware the bosses and Instakill Mooks

According to Television Tropes and Idioms, the so-called Instakill Mooks are foes all about one-hit kills, therefore being capable killing the player character in a single hit (no matter how much HP the victim may have).

In many mini-games with Perspective Flip, the player character is a human being (quite suscetible to one-hit kills), whereas the boss in mook clothing and demonic spiders (pretty much all of the generic monsters) have the deck stacked in their favor.

Wearing a powered armor doesn't protect from one-hit kills.

Much like Shade from Evil Within (above), certain monsters tend to play cat-and-mouse with the player character, and one of the most fearsome examples is Lenin himself.

Afraid of the albino Komodo dragon? The generic monsters are even more dangerous!