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Scenario Model: Opening or Closing the Portal

by Mike on 28 October 2024

Like the adventure models in the Lazy DM's Companion, sometimes it's useful to have models for more specific scenes or encounters in our 5e RPGs. Today we're going to dig into one such scenario model – opening or closing a portal to another world. This model is both a common situation and a fantastic one, one in which all the characters can be challenged to either close a gate that shouldn't be open or open a gate that shouldn't remain closed.

Something for Everyone

It's important that players and characters all have something to do in a situation like this scenario. We don't want some character just sitting back or spamming the same ability over and over. We also want to mix up the activities, sort of like traveling through the wilderness, so that everyone has a different type of activity.

The In-World Situation

Instead of jumping straight to mechanics, we want to understand the situation as it is in the world. First, we have a big ancient gateway – one that isn't entirely stable. It's old. It's cracked. Energy leaks from it when it's active – energy that must be dealt with somehow. Also, things can get through. Whether you're opening it or closing the gateway, it attracts things – not very nice things. Maybe these things come from the world beyond and that's why the group wants to close it. Or maybe these things come from somewhere else. Maybe there are cracks in the edges of the portal leading to other worlds best left alone.

The portal can be powered by several arcane anchors – pillars with crystal spheres or glowing runes set outside of the portal. Channeling arcane or divine energy into these pillars activates them or, likewise, can draw energy out of them when trying to close the portal. Pouring energy or drawing energy out of these pillars has a nasty tendency of projecting the energy of this portal to those nasty things we talked about earlier – they want to get through the portal really badly.

The Roles

With this understanding of how the portal operates, now it's time to think about how to deal with it. Someone needs to channel energy into the pillar or portal to pull energy out. Those characters best suited to this task are those characters who are either trained in arcana or religion or who can cast divine or arcane spells. This channeling takes an action to begin but only a bonus action to keep it going. It does, however, require concentration. If concentration is broken, the instability of the portal grows violent.

The difficulty class of the check to succeed at this action is based on the state of the portal. If it's in reasonably good shape, it might only take a DC 10. If it's really coming apart it might take a DC 15. Channeling the energy of a spell always succeeds in opening or closing the portal but failing at the ability check causes instability. A blast of lightning might arc out from the pillar and strike the channeler or even someone else. It might target a wild magic surge on someone in the chamber.

Divine and arcane casters can choose to use their spell slots to reinforce their checks. For each level spell they want to expend, they can reduce their check for the round by 5.

And, of course, things are coming out of the portal. They probably start coming out as soon as the channeling begins. These things might be demons, devils, aberrations, or undead – all seeking to sink their fangs or wrap their tentacles around mortal flesh. That's where the other characters come in. The other characters have to hold off these monsters from the channelers.

We can give defenders a new reaction here, the "dive in front", reaction. If a creature attacks a channeler in the area, the defender can take their reaction to dive in front of the attack and save the channeler.

After three or so rounds, the portal is successfully opened or closed. This scenario assumes it's critical that the characters succeed, so instead of having the gate fail to open, it simply brings on more pain on a failure. A TPK is still possible, of course.

Scaling the Encounter

This encounter probably works best at 5th level and above since it takes a lot of coordination between the characters. You can use the Lazy Encounter Benchmark to get a general idea how many monsters might be inadvertently deadly. You can also break up monsters into waves. A few small creatures on round 1, a couple of bigger creatures on around 2, and a boss on round 3.

As far as the amount of damage the pillars might inflict, we can use the following guidelines for each tier for blasts of energy (fire, cold, force, necrotic, or lightning – your choice):

Tier 2 (5th to 10th level – CR 8). +7 to hit, 28 damage.
Tier 3 (11th to 16th level – CR 14). +10 to hit, 49 damage.
Tier 4 (17th to 20th level – CR 20). +13 to hit, 70 damage.

A Reusable Model

You probably don't want to use it every session but this model is generally reusable for this common situation – opening or closing a portal. The model focuses on what it's like in the world, some interesting roles for characters to take, and a fun situation with lots of moving parts. Hopefully this model gives you a nice scenario you can drop right into your own game.

More Sly Flourish Stuff

Last week I posted a couple of YouTube videos on One Year with Shadowdark and Expanding Doom Points from Tales of the Valiant.

Last Week's Lazy RPG Talk Show Topics

I was away at Gamehole Con, which was awesome, so there was no Lazy RPG Talk Show last week. Sorry! You can enjoy past episodes and subscribe to the podcast)

RPG Tips

Each week I think about what I learned in my last RPG session and write them up as RPG tips. Here are this week's tips:

Avoid damned-if-you-do, damned-if-you-don't choices too often. Offer choices with a clear gain and risks.
Limit source material to focus a campaign and make it unique among all other campaigns.
Check in with players every few sessions to make sure your game is headed the way everyone enjoys.
Keep track of magic items distributed to which characters. Better yet, ask a player to quartermaster and post the distribution.
Build characters from the story and situation first. Then measure against potentially deadly benchmarks.
Index cards and a Pathfinder Basic Flip Mat are hard tools to beat for improvising your game.
The d20 is a swingy die. Don't expect it to behave the way you want. Plan for and enjoy its high randomness.

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