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Modifying Spells to Make Traps

Dark_corridor_(4676385338)Sometimes, you want a desired effect for a trap that *almost* mimics a spell, but you’d like to make some changes. How do you do this? Let’s look at the following trap.



Semi-Permeable Wall of Force (CR 8)

A dark corridor leads south.

Type: magical; Perception DC 32; Disable Device –

Trigger location; Reset None


120 feet down, the corridor ends. However, the beginning of the corridor is blocked off with a semi-permeable wall of force. This acts just like a normal wall of force spell at CL 13, except that it allows movement through it in one direction, and prevents movement through it in the other direction. The characters can freely pass through it, but won’t be able to move back through it out of the corridor.

This trap is essentially a wall of force with a slight modification. As per the trap creation rules, the CR of this trap would be spell level + 1, and the Perception and Disable Device Checks would be 25 + spell level. Normally, a wall of force is a 5th level spell. However, this is a special wall of force that allows passage through one side. The closest mechanic would be a meta magic feat that modifies the spell. Normally, these would use a spell slot of a higher level. Looking at the various meta magic feats, it seems reasonable that this modification would use a spell slot 2 levels higher.  So, in this case, our wall of force spell is now a 7th level spell, yielding a CR of 8 and a DC of 32 for Perception and Disable Device.

Since this is a static effect, there is no saving throw to avoid the effect, neither is there Disable Device check for this particular case, as this trap is not triggered or set off by the character’s actions.

Most players can meta game around normal spell effects. However, if you modify the spells in your own unique way, they won’t be able to meta game around them. Also, as an added side bonus, you’ve now introduced some new mechanics and new ways to trap your players. Next time they run into what looks to be a “normal” spell effect, they may think twice before blindly rushing in.

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Using Spells in New Ways – Lake Barrier Trap

Škocjan_Caves_lakeOne way to get inspiration for a trap is to look through the list of spells available to spell casters. Pick one, and then try using it in an interesting way, and perhaps tweak it a little bit to fit the effect you are going for. Take the following trap for example, which is based on Antilife Shell.


Lake Barrier Trap

The cliff edge overlooks a placid lake, dozens of feet down.

Type: magical; Perception DC 31; Disable Device 31

Trigger touch; Reset None


The lake below is cold and deep. It has also been covered with a type of antilife shell. Non-living stuff passes through it just fine, however, when someone jumps… Lake Barrier (6d6 falling damage)

It’s hard to get players to walk into traps. You could use a wall of force here, but a clever player will throw down a rock or do something else to discover it. Unless the players use detect magic or something, they probably won’t notice this. Add some kind of “pressure” element at the top, and the first one that jumps will be in for quite a surprise.

However, the true payoff for this trap, whether is damages players or not will be the next time they come across a similar setup. Perhaps the mage will start carrying around a satchel of gerbils to toss of the cliff before descending. These are the types of experiences that make adventures truly memorable. “Hey, remember that time when you summoned a dire rat in mid-air just to check to see if there was an anti-life shell?”