Perhaps the biggest addition to gameplay is the grappling iron, coded by Talon and modeled/skinned by Heretic Hides.  It allows the Ogle to latch onto nearly any wall a certain distance away.  The grapple is given to the Ogle early in the game so that the player can spring out of harm's way when necessary.  Some areas, though, like cramped areas, offer no escape.

I wanted the monsters to feel embedded in their environment, like they know the area better than you, because you're just passing through.  Certainly they know how many of themselves are needed to stop you from continuing on.  This is what I call "situated AI," or the AI linked to intrinsically tying a monster to its environment (instead of relying on coding in the monster itself).  Given that Heretic II is a fairly old game, I hope you'll notice my philosophy at work in this aspect of level design.