One area of game difficulty which lies in both the hands of the players and the game master is the game’s monsters or antagonists.
You might think that “monster difficulty” lies firmly in the hands of the GM, but this is only part of the answer. In a campaign where undead feature prominently, the difficulty faced by the party will be proportional to the number of priests in the group — armed with turn undead and similar effects.
Foes armed with powerful magic — demons, dark elves, and sorcerers, among others — will be more difficult to defeat without one or more magic-users in the party. While a group of fighters may chip away at a stoneskin effect, they’re far more likely to fall to a barrage of illusions and mind-affecting spells.
So here is another area where player choice has an effect on the game difficulty — while the GM will ultimately choose the monsters to include in a given adventure, it’s the players who choose which tools they bring to bear, and of course whether to engage monsters or flee. Better part of valor and all that.
Part of my goal in creating tiers for monsters (the scope system I’ve discussed before) was to ensure that monsters of each type bring a consistent level of challenge to characters. A number of different systems have been used in the past to try and reflect this idea — each with its own advantages.
Challenge Ratings in 3e were used to put monsters with vastly different Hit Dice and Special Abilities on the same page. And it worked effectively for the “average” encounter, unless you pushed the system to the extremes.
4e’s monster levels worked on the opposite principle of Challenge Ratings — instead of one monster being a challenge for a group, one monster was a challenge for one character. Instead of pitting one monster against a group, you used a group of similar size to the player characters.
This system also worked unless it was pushed to the extreme limits — or admittedly, much beyond the Heroic tier at all. Paragon- and Epic-tier foes couldn’t compete for the most part. But the system worked really well.
What those higher-tier monsters seemed to lack were special abilities that operated outside the normal realm of character powers. In the end, “damage is only damage,” and by the Paragon tier — players have a handle on “damage.”
Level Drain, Ability Damage, and Item Destruction would seem to be three basic areas where Paragon- and Epic-level monsters could shine. Instant Death effects really seem only an extension of the “damage” system, whereas losing a few points off of Strength or losing a weapon are scary in a very different light.
Insubstantial or incorporeal creatures pose another interesting dilemma, which was solved by magic weapons in 3e — but was sadly weakened or ignored in 4e by appearing as a mere damage modifier.
Laundry Files has an interesting method of dealing with insubstantial creatures — as they often appear as “possessors” in encounters, they are typically un-killable. The vessel of an incorporeal creature may be disabled or destroyed, the entity may be bound or banished — but they cannot be directly harmed.
To offset this incredible advantage, the majority of incorporeal creatures can maintain a presence in the material world for a limited time without possessing a physical host or body. This treatment of insubstantial creatures (which don’t even have hit points) really lends itself to creating a sense of existential dread.
Another area for monster development might really be in “size.”
Games like Shadow of the Colossus and Dragon’s Dogma show us how joyous more interactive monster fights can be — scaling a cyclops to bury a spear in its eye, or grabbing hold of a gryphon before it takes flight — these both sound like highly entertaining encounters, but they require a different scale of play.
It seems tedious and short-sighted to bring a giant down by hacking at its knees. And restricting this kind of play to characters with high grapple modifiers seems arbitrary. The question to ask though, is “how?”
All of these questions are related to how monsters can define the difficulty of a game — the role that player choices have in modifying monster difficulty — and where games succeed or fail in providing variations in challenge.