Is there a correct way to deal with "fish-in-a-barrel" type combat?

Question

I'm wondering if there is an official way of dealing with "fish-in-a-barrel" type combat, and if so, what is it?

Examples:

Some examples might include:

• Monster in a cage and the PCs want to stab/shoot it
• Monsters in a pit and the PCs want to shoot them from above
• Monster hanging helpless in a rope trap

Basically any situation where the PCs have a way of attacking the monsters without fear of retribution (or vice-versa).

Initiative or no?

My big question revolves around whether or not I would ask for initiative rolls. Would we go through initiative order and when it is the trapped player's turn they are just unable to do anything to fight back, but continue going through combat order until they are killed? Or would I avoid initiative and just let the PCs kill without actual combat?

Specific scenario:

This question has come from a scenario I'm planning in an upcoming one shot. The room is intended to be a test of resourcefulness, and it will have a large pit that needs to be crossed that contains poisonous snakes. But I was thinking of including access to a secret room that the PCs wouldn't discover unless they climb down into the pit and dispatch of the snakes.

And so I wonder: Are there any game mechanics in place that could prevent my PCs from just standing on the edge of the pit and shooting all the snakes with arrows?

Answer 1

I’m going to fall back on the same advice I offer for skill challenges, which is to say, I am going to suggest checking out Angry GM’s 5 Simple Rules for Dating My Teenaged Skill System (warning: mild, censored swearing of the $^#% variety):

Only roll when

1. There is a chance of success

2. There is a chance of failure

3. There is a cost to failure

This is a situation where there is no chance of failure. That’s the entire premise of the question. Oh, sure, there’s a chance of failure on any individual roll, plus there’s a question of “how much success?” in damage rolls, but none of that matters here because they can, and presumably will, just keep trying until they succeed. That means there is no chance of failure here, in a vacuum.

The only question here is time, which leads me to a huge important takeaway from Angry’s suggestion: lost time is only a cost if time is clearly and obviously crucial. If the mad cultist has chained up some beast for sacrifice in some horrible ritual, and the players seek to thwart him by putting the beast out of its misery first, then it’s a race between the players trying to kill it and the cultist trying to get the ritual completed (or at least up to the point where the players killing it would just complete the ritual). Then time matters. Other scenarios might have time matter.

But most situations, time doesn’t matter, or matters only in abstract or distant ways. And if the player characters don’t know about the time pressure, then it doesn’t count either—they don’t know so they should have no reason to let that affect their decisions. And if they aren’t making decisions, they aren’t roleplaying, which in a roleplaying game, means they aren’t playing the game. They’re playing “roll the dice and tally the numbers,” which really isn’t the game.

(Conceivably, ammunition could matter too, but most of the above also applies to ammunition—in most games, most of the time, mundane ammunition is plentiful and not worth worrying about as a limited resource.)

Don’t spend game time on not playing, as much as you can help it.

So no, in these situations, when the players announce their intention to do so (and how they’re going to do so, in cases where it takes some cleverness), just say it happens. It’s a foregone conclusion. Describe it narratively as appropriate, and move on with the game.

Answer 2

Try not to engineer situations like that

Generally, such a thing is not a challenge and the players would only be motivated to do such a thing to farm XP. You could declare that because it's not a challenge, they will not get XP for it, although if they are removing a hazard (i.e. in your pit of snakes example, if there was a key or some other McGuffin they needed) then awarding no XP for finding a way to progress would not be such a good idea.

However, in your specific example, it doesn't need to be a fish-in-a-barrel situation. Consider including tiny holes in the walls at the bottom of the pit that the snakes could rush into if they are attacked with no way to defend themselves; that way, the PCs can't kill all of them from up there, and the only way to "continue combat" is (for at least one of them) to go down there, at which points the snakes can actually attack someone.

If this needs to be justified by combat rules, you can say that the snakes have readied an action to "run" (slither?) and hide in those holes, the trigger being if they are attacked.