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How to use portals as an exploding device.
Getting a protal to function as a bomb is all about how you define them in your game world. My definnition is as follows:
Whether they are doors for travel or only windows for scrying, portals are tight pinches in spacetime (in a science fiction world, characters would call this phenomenon an artificial wormhole).
It takes an incredible amount of energy to bend space into a functioning “link” – usually more than a caster can channel at one time. (Just as in a block and tackle, where a small force is multiplied by a greater number of pulleys and a greater length of rope to lift a heavy load, portals are usually created with over a lengthy amount of time, using a moderate amount of magical force). Therefore, if the portal is destabilized all at once, the energy release (not to mention the reverberation of spacetime springing back to rest) is tremendous.
There’s your explosion. Depending on the “size” of the portal (e.g., how far the link goes times how large a being can fit through it) it might take out a whole building or a whole county.
Setting one off
Conveniently, there’s always an expert around with the know how to
The mechanism they use to do this is up to you. In my game, the NPC du jour got an Orb Of Cancellation out of the strongbox and lobbed it into the portal.
What’s crucial is that the process takes time – because the whole point of a countdown scenario is that the players get to rush around looking for a solution. Perhaps it’s a ritual being chanted by a mage as the party fights their way to him, or perhaps the spell can be performed quickly, but the construction of the link is strong enough that it takes time to wear down.
Possible Countdown Mechanisms?
How to the PCs know how much time is left? The “roll your magery… you can tell it has 60 seconds left” is kind of boring.
Instead, when the party mage rolls (which he ineviably will) tell him that he knows the crystals in the portal’s physical framework are supposed to be clear but are turning dark. This provides the group with an essentially readable countdown timer – whenever they ask how much time is left, describe increasingly darker colors: red, to purple, to blue, to black.
You can also introduce environmental hazards as the countdown continues: lightning, fire, and icy wind can blast the party as reality is torn apart.
Reversing the Collapse
Ah yes, the solution to the puzzle.
Sure, you could write down ahead of time a specific DC they must exceed on their Magery roll in order to perform a successful Disarm, but why bore yourself?
After I give the group the basic info (the portal definition above, in this case) I’m a big fan of sitting back and listening to how the players think something works – then creating a solution organically. If the party scholar asks, “What, exactly, is powering this thing?” I say, “Well, you’re the resident expert in arcana, how do you think it works?” Once you get ideas on the table of how the thing works, theh players will start thinking of clever solutions. You can leave those up to dice rolls if you want – because at that point they’re not just solving your puzzle, they’re doing something they thought of themselves.
In my game I provided a no-win solution. There was a re-stabilizing spell (the party mage would either know it or be able to find it nearby), but the portal would be too far gone to do anything except lessen the blast – and the chanter would have to stay within the blast zone to do it. This would give some great roleplay opportunity as one PC would step up to buy time for his friends to escape. (and in the end, that guy found a solution that was even more memorable and badass
Have a possible solution or two in mind. But encourage roleplay, exploration, guessing, and world-building instead of just telling it to them. And then be willing to change it according to the ideas they’ve laid on the table.