Players can’t have perfect agency. The rules of the game don’t allow it—technically, anything that requires a roll prevents the players from having full knowledge of the results of their actions. But players generally believe that when they make a decision, that decision will have some consequence on the game, whether the consequence is “we have ascended to godhood” or “my turn accomplished nothing but verifying that the monster is, in fact, immune to slashing damage.” They accept some unpredictability for the power to make meaningful decisions.
This is what makes the quantum ogre such a sneaky DM tool. While it’s a useful trick for a DM who wants to give players freedom but limit the effort he needs to put into providing it, it is still, in the end, a type of trick. It removes some of the meaning from their decisions by predetermining some of their consequences. But this isn’t necessarily a bad thing. By easing the impact the quantum ogre has on the players’ choices, it becomes less of a heavy-handed railroading tool and more an agent of convenience for the DM.
The quantum ogre is an encounter or situation that occurs regardless of the players’ decisions. It refers to the concept of quantum superposition, and in this use it’s meant as “an ogre who exists in multiple states until observed”. That is, the DM designs an ogre encounter, but he doesn’t decide when the encounter occurs. It’s always there, waiting, until the DM springs it on the players as though he always intended for it to happen at that time. Sometimes it’s obvious, as in this example from a few posts ago:
Consider a traveling party who comes to a crossroads. They head west, enter a forest, and find a dark cave littered with bones and signs of troll habitation. If they instead head east, the path takes them among a beach, where they find a dark cave littered with bones and signs of troll habitation. Regardless of where the players go, the DM planned a troll cave, and that’s what they’re getting.
When done right, the quantum ogre is basically invisible. Say our players didn’t see any signs of a troll cave. Say they’re just moseying along, minding their own business, when a troll lumbers out of the woods to fight them. In this case, the players didn’t exactly have their decisions circumvented or overridden. They wanted to enter the forest, and they did. It’s just that a troll was going to lumber out of something and attack them whichever way they went. They didn’t know the encounter was written in stone, so they don’t feel like their agency was violated.
But, technically, it was. Agency involves making meaningful decisions, not just decisions at all. Here the players didn’t know their choice wasn’t actually meaningful, because they didn’t have sufficient information to make a choice that determined the encounter they would meet. The players didn’t actually have agency, they had the illusion of agency—they thought their decision had meaning.
Is this a problem? Well, yes and no.
If you consider full and complete player agency to be the ultimate goal and intent of a tabletop game, the quantum ogre is an obvious sin against the social order and it has no place in the game. But, by and large, D&D players don’t think that. Players tend to value certain things over perfect agency, including but not limited to unpredictability—the tension of not knowing the result of an action until a die hits the table—and immersion—the practice of acting consistent with a character’s knowledge or lack thereof. A good game balances all this. Imagine a fight in our troll cave. Perfect agency means telling the players that a troll is ahead, it is weak against fire, it has 84 hit points and AC 15, and it can make three attacks per turn with a +7 attack bonus, so the players can make all of their decisions with as much knowledge of their consequences as possible. Perfect immersion means letting the players walk up to the troll, wail on it for a while, realize they have no way of knowing how it regenerates because their characters have never heard of a troll before, and possibly die before they can escape. Perfect unpredictability means the players fight the troll, but now the floor is ice and the players are rabbits and their torches make fun of their weight. None of these is especially fun.
For the average group, the quantum ogre is a tool like any other. It’s a micro-level railroad, invisible to the players, and it’s mostly used to give the DM a break. He can plan one quantum ogre encounter instead of designing several encounters for the various paths the players might take or determining it on the fly in the middle of the session. It lets him avoid the unpredictability and narrative hollowness of a random encounter table, and he can lay plot seeds or campaign lore into the encounter and know his players can’t miss it. It’s a perfectly reasonable way to keep the game running and save the DM some time and effort.
That said, there are right and wrong ways to use it. When overused or obvious, it can make the players feel like their actions don’t mean anything. This most often happens when the encounter itself doesn’t occur, but signs of it do. If the players hear about trolls on the west path, and they deliberately take the north path to avoid the trolls, it’s bad form to give them a troll fight anyway. The location of the trolls was, effectively, “observed” by the players when they heard about it even if they didn’t experience the encounter themselves. Even if you have perfectly valid story reasons to put trolls on both paths (for example, the trolls historically have only lived in the west, and their presence in the north is a sign of a change in their ecology), don’t give the players only half the story then punish them for not knowing the rest. At least tell them there have been recent signs of trolls in the north. The players and characters will both be prepared for the fight and they won’t feel like you’ve subverted their planning.
You can also make the encounter itself dependent on what the players do. The quantum ogre is assumed to be a static encounter; there is an orc warrior with a greataxe, and he has two goblin allies with shortbows who snipe at the party from the trees while the orc draws all the attention. But it doesn’t have to be static. You can have one static element, like the orc, and move everything else around it. The players retain some agency in that their decisions determine what the encounter is and how it plays out, but the DM doesn’t have to build a whole combat on the fly or design several of them top-to-bottom.
Adjust the amount of dynamism in your encounter design based on what you’re comfortable with. Even the smallest change can lead to a drastically different encounter. If the players go one way through the forest, the orc has an greataxe and the goblins have shortbows. If the players go a different way, the orc has a longbow and the goblins have spears. The monsters themselves are exactly the same, but different creatures with different threat levels want to engage with the party in melee. You’ve gotten two fights out of one concept and one group of stat blocks.
With more dynamism, this becomes more powerful. To start off, the orc doesn’t have to come with goblins. If his allies are wolves instead, now he’s a hunter who wants to lure the party into a trap. If his allies are weaker orcs, he might be teaching them or willing to use them as a distraction while he flees. If his allies are something strange and exotic, like mephits, his overconfidence might show in his tactics. All of these assume the orc even wants to fight the party, and he could instead try to barter with them or ask for their help. Or the terrain could be different, and if he meets the players in the mountains he can attack from elevation or hide behind boulders. Or he has different emotional states, and the orc by the river is full of bluster while the orc in the tundra is hungry and desperate. If you leave gaps in the orc’s stat block, like deciding he has proficiency in a skill to be determined when he appears, you give yourself even more room to tweak him as you need. “The players will fight an orc and its two allies” is incredibly open-ended, and you can fill in the gaps only when necessary.
The best way to do this is to tie it in to what the players know before and/or after the fight. Let their decisions matter, not just in the background but visibly and directly. Tell the players that goblins are on one path and wolves are on the other, and an orc/goblin or orc/wolf fight makes perfect sense. Tell them how the terrain might affect their combat strategy, and they’ll be ready to mitigate (or take advantage of) tree cover or clear lines of sight. If you do spring something weird on them, and suddenly they’re fighting a hungry orc with a crossbow, let them treat it as a plot hook. Maybe the orc appears hungry and desperate, and when the players dig deeper they find something wrong with the animals he usually hunts. Ideally, take advantage of both pre-encounter and post-encounter knowledge; the players have heard about poor hunting results in the west, so when they go west they fight a semi-planned orc with his wolves, and they notice the wolves don’t share the same symptoms as the deer so they conclude that the source of the sickness is the plant life. If they go north, where people have been disappearing, they fight the same semi-planned orc and his dretch allies, and they start thinking a demonic cult might be involved. You have plenty of time to figure out the specifics of the storyline later, once the players are committed to it. Plan half of an encounter and use it as a quantum ogre, filling in the rest to lead whichever way you need at the time.
A bad quantum ogre takes control of the game away from the players, invalidating their choices and laying things out like a video game. A good quantum ogre adds to the story and lets the players affect what they do but doesn’t force the DM to prepare an inordinate amount of content. It’s the same principle as loose session design: plan as much as you need, but no more, and give yourself a way to quickly fill in anything you intentionally left open. This does limit the players’ agency in that they don’t have total control, but it’s a small concession against the backdrop of an entire campaign. Use it sparingly, use it well, and it’s a great tool to keep in your box.