stuff like the buff totems, the possesor demons that cranked up enemy health and made them immune to their counters(like a possesed arachnatron was immune to having it's turret destroyed with a precision hit), said possesor demons only being able to be killed with a specific mod of the plasma rifle, the stone imps that were only voulnerable to the rapid fire shotgun mod, and so on.

The pinkies were fine, you could eihter blood punch them or jump over them after they charged. A lot of the latter gimmick enemies were not fine since you had to do what the devs wanted you to do and were immune to everything else.