Illusions, Duration, and Mobility

Illusions, Duration, and Mobility

I might have been doing illusions wrong.I got asked "Eggplant, you dumbass, why does your Mirror Image say that your illusions cannot move? There is nothing in the statline that would imply that." At first, I wanted to tell that person to blow it out his ass, but then I realized that I might be the one who needs to do that. Then I looked at the Illusion advantage more closely and realized that this is one big mess that needs untangling. Let's see.

First, let's see the culprit.

Illusion is found on page 94 of GURPS Powers. 

Activation: It requires a Concentrate maneuver to activate without a die roll.

Duration: Illusions persists for as long as you concentrate (which means consecutive, uninterrupted Concentrate maneuvers).

Range and Area: By default, illusions appear in a two-yard radius around you.

Question: Does this area move with you? After all, Concentrate allows a step, so you would be able to step out of the initiale area in two turns and "lose" your illusory gun (Sidenote: This example given in the description is strange. After all, Concentrate is an obvious maneuver, so you would be unable to do anything with the illusory gun in your hand.).

Answer: I don't know. Nothing in the description of the advantage is explicitly said about this. My gut feeling is that it should, even though I treated it the opposite way before. Of course, you could move an illusion smaller than its entire area effect within the area of effect, but this is not what is being asked.

Let's take a look at the modifiers.

Independence (+40%) makes it so you do not need constant concentration (now you can do stuff with your illusory gun). Your illusions can respond in simple way, but you retain the ability to Concentrate to change them.

Please note that this is not the same as the generic Independent (+40%) enhancement from the same book! The latter is not compatible with unmodified Illusion, as it requires no die roll and does not have a fixed duration. In addition, it forbids controlling the parameters of the advantage, which Independence does allow you a degree of control. However, Independent explicitly says that it "doesn't allow multiple instances of the advantage's effects unless this is standard for the trait."

Which begs the question - can you create multiple instances of Illusion with Independence, +40%?

The answer is both "yes" and "no."

If the area of effect did not move with you, you would be able to spam the everloving crap out of this advantage and cover everything you walk through with illusions that do not need constant concentration (but that still disappear if you fall asleep or get knocked out). This doesn't feel like intended behaviour.

If the area of effect does move with you, then this thing looks fine, doesn't it?

But why don't we look at precedents of premade abilities based on Illusion? (Although, nowadays I am slightly skeptical of this approach, because I keep finding more and more mistakes in premade abilities). Let's start with the same book and open page 140 of GURPS Powers.

Images (+100%): Illusion (Area Effect, 4 yards, +50%; Independence, +40%; Ranged, +40%; Visual Only, -30%) [50]. Notes: Generates believable, fire-and-forget illusions at a distance.

Wait, what the hell is this? "Fire-and-forget"? Doesn't that imply that you can create multiple instances? Perhaps, we should take a closer look at Ranged, +40%. It's found on page 107 of GURPS Basic Set. There is some extra stuff on page 105 of GURPS Powers, but nothing relevant. Ranged states the following: "Duration is 10 seconds, unless the ability lists another duration (like Neutralize or Possession) or is instantaneous (like Healing), and you cannot use the ability again until all existing effects have worn off." Illusion does list "another duration", because it is an indefinite one, so the ability in question can create only one fire-and-forget illusion that isn't really fire-and-forget, because it's an indefinite duration ability that will be turned off if you become unconscious.

Let's find another one. Hologram from pp. 35-36 of GURPS Psionic Powers. (Sidenote: If you inspect psionic abilities in this book closely, you'll find some clear mistakes and some baffling decisions in some places. Despite that, I love the book). The statline reads the following: Illusion (Ergokinesis, -10%; Environmental, Light, -10%; Nuisance Effect, Range is actually 5 yards, -10%; Ranged, +40%; Reduced Range 1/10, -30%; Requires IQ Roll, -10%; Visual Only, -30%) [10]. This is another Ranged Illusion, but without Independence. However, there is a technique that adds this enhancement. Nothing is explicitly said about multiple instances, although being limited to one instance is implied.

Is there anything else? Complex Illusion from page 18 of GURPS Thaumatology: Sorcery. The statline reads the following: Illusion (Independence, +40%; Ranged, +40%; Sorcery, ‑15%) [42]. Now let's take a look at the duration. It says "Indefinite", which means that you cannot have multiple instances of it.

There are a few other examples, but they do not bring anything new into the question. One thing to note is that there are no premade examples of Illusion without Ranged, so we have no explicit answer to the initial question of whether the area of effect moves with you or not! I'll say that it does, because otherwise it feels stupid.

Now, there is another question, how do you make real fire-and-forget illusions. That's easy, you add Persistent, +40% (p. B107) and Independence, +40%. While GURPS Basic Set says that you can only add it to attacks, GURPS Powers adds that it also can be used for other abilities that affect an area innately, and Illusion fits the bill. While nothing explicity forbids you from taking Persistent without Independence, they feel incompatible to me. However, even though this is a fire-and-forget Illusion that you can have multiple instances of, you can still Concentrate to change them. Yeah, Persistent doesn't remove that, and Independence explicitly allows it. To remove this capability, I would add Nuisance Effect, Cannot alter the illusion after creating it, -10% (similar to Cannot concentrate to extend duration, -10% on some Control-based sorcery spells from GURPS Sorcery: Protection and Warning Spells).

So, there's that. Nothing explicit, but everything seems to point to the fact that the area of effect does indeed move with you. So, I was doing some of my illusions wrong and now have to correct them.