“Are you ever not going to fall for that?”
— Loki, The Avengers (2012)
The Illusion advantage (GURPS Powers, p. 94) is probably one of those things that should have been in the Basic Set, but wasn’t.
Illusion as Pieces Parts:
So what does Illusion do and how does it do it?
- This requires a Concentrate maneuver to use, but not special die roll.
- You can create animated, 3D images of anything you can visualize in any spectrum you can see, with sounds you can normally hear.
- To deceive another with your illusion roll a Quick Contest of your IQ vs. their Perception. Success means that illusion seems real to the victim. The GM decides how NPCs react, PCs decide how they react. You have to make a new Quick Contest if your victim interacts with the illusion in a way that wouldn’t be possible (e.g., sticking your hand through an illusion of a wall)/
- Sometimes a skill roll is required instead of just an IQ roll. This is often Artist (Illusion)
- Illusion can be used to cause a Fright check, but you must win a Quick Contest of Artist (Illusion) vs. the higher of IQ or Perception.
- Base Area is 2 yards round you (this can be a smaller area if you wish).
- If your final modifier (see below) is a net bonus and your victim is aware you have powers, but not what those powers are, halve them!
+4 if the victim is warned by someone else who knows the illusion is not real (or if you critically fail a role against someone else).
+10 if you create an illusion unsubtly and in plain sight.
+1 to +10 for an inappropriate illusion.
-1 to -5 for a believable one (e.g., you pull out a thermal detonator).
+4 per fake person after the first (cumulative).
Rules as Written Illusion Special Modifiers
A short list of modifiers for Illusion appear below, but here are a few generally useful ones. Reliable (GURPS Powers, p. 109) will allow you to more easily dupe your victims. Area Effect (GURPS Basic Set, p. 102) will allow you a larger radius. Ranged (GURPS Basic Set, p. 107) allows you to project illusions at a distance. Low or No Signature (GURPS Basic Set, p. 106) could reduce (or remove) the penalty for creating an illusion unsubtly and in plain sight. Persistent (GURPS Basic Set, p. 106) allows your illusion to last for 10 seconds after you concentrate (add Extended Duration normally for a longer time).
- Auditory (-70% Limitation: GURPS Powers, p. 95): You can only create sounds.
- Broadcast (+50% Enhancement; GURPS Powers: The Weird, p. 33): Requires Mental, allows multiple people to see the same thing at once. Uses the same rules as Broadcast under Telecommunication (GURPS Basic Set, p. 00)/
- Cosmic, Can heal as well as harm (+50% Enhancement; GURPS Powers: The Weird, p. 21): You can heal injury to the subject equal to your margin, but you must have Mental and Stigmata and suffer a -3 to repeated rolls doing so. See below for a breakdown on why this should probably be a +100% modifier, not +50%.
- Extended (Variable; Enhancement; GURPS Powers, p. 95): Let’s you fool senses other than auditory and visual range (including aural and visual ranges you don’t have). Totally new senses cost +20% a level.
- Hallucinating (-50% Limitation: GURPS Psionic Powers, p. 14): You don’t control what the victim sees, you treat them as if they were hallucinating (p. B429).
- Independence (+40%; Enhancement; GURPS Powers, p. 95): You no longer need to concentrate to maintain an illusion.
- Initiative (+100%; Enhancement; GURPS Powers, p. 95): Gives the benefits of Independence and gives illusory people the semblance of free will. They act with your DX, IQ, and skills.
- Mental (+100%; Enhancement; GURPS Powers, p. 95): LEt’s you project images into a specific target’s mind. This works on anyone you can see or touch; you take a -1 per person affected.
- Static (-30% Limitation: GURPS Powers, p. 95): Your illusions are unanimate stilllife images.
- Stigmata (+100%; Enhancement; GURPS Powers, p. 95): Allows you to use your ability to hurt someone else, but not if they are unconscious. Add a +300% Cosmic, Irresistible Attack to ignore even that if you want to be Freddy (WELCOME TO YOUR NIGHTMARE, BITCH!).
- Visual Only (-30% Limitation: GURPS Powers, p. 95): You can only create images.
The Curious Case of Cosmic Chimeric Chirurgy
GURPS Powers: The Weird has some unusual abilities – most of them special cases of Cosmic with a few odds and ends. During the playtest of this book I stringently voiced many opinions on the power builds, and that doesn’t disclude this new modifier for Illusion. First, it is weird (and that’s ok, because that’s the book), but it’s not fairly priced. It’s a pure math issue, in order to do what The Weird suggests (a Quick Contest lets you heal your target your margin in HP). Powers suggests that a subject of a beneficial ability can simply wave his roll to resist (see p. 40 of that book). Since Healing has no opposed roll it gets weird for actually someone with this Illusion enhancement, you might actually heal them at all if you read it strictly and nothing requires that you have to resist an ability (though some advantages such as Magic Resistance force you too as trade off for their protection). So let’s just assume that you can heal a subject normally with a roll; i.e., they choose not to resist. This means that you can make an IQ roll and instantly heal them (on average) your IQ – 11 points of injury. If you pretend to be a doctor or performing First Aid you can get a +1 to +5 bonus to your roll (inverted from the normal penalty to your target’s roll as they are not resisting). Oh, and you also can do this while projecting illusions into people’s brains that can kill them. It’s like saying “I have an Innate Attack that can hurt you or heal you.” But that’s not were it breaks down for me. Healing this way costs no FP unless you add that as a limitation. Since most folks are going to heal at most 12 HP your Healing advantage would look like this:
Healing (Capped, 6 FP, -10%; Injuries only, -20%; Reduced Fatigue Cost 6, +120%; Requires IQ vs. Will roll, -10%) 
Now, you need to also take into account that Stigmata and Mental are prerequisites, Soyour build looks like this:
Illusion (Mental, +100%; Stigmata, +100%; Cosmic, Can heal as well as harm, +50%) 
So the effective cost is 38 points if you take away the ability to create illusions (-25 points for the base ability) and hurt others (-25 points for Stigmata). So it’s still cheaper than a comparable Healing ability. Gamers using this would be better off using a +100% modifier as that’s much fairer (or even +75% if you’re willing to use in between values for Cosmic modifiers) than +50%.
New Modifiers for Illusion
Some new modifiers I’ve posted on the forums or use in my own game:
- Can Be Damaged: Your illusions can be damaged and thus disrupted. Your illusions have HP equal to your Will/3. At 0 HP, it disappears. If your illusion is ever destroyed it takes another minute for you to use your ability again. If you’ve created multiple illusions each one disrupted gives others a +4 bonus to disbelieve your powers and an immediate roll to to disbelieve. -50%. If your illusions get DR equal to IQ/3, this costs -30% instead.
- Chronoception: Your illusion alters with the subject’s sense of time. This requires Mental (to affect time itself buy an appropriate Control!). Each level allows you to speed or slow the victim’s perception of time by a factor of ±10 (e.g., 3 levels would allow you to speed time up by 1,000). This can only be used to follow a subject into thinking something happened. You can’t use it to actually age them! +30% per level.
- Cosmic, Extended: Your illusion hits the target so fully that all of their senses are affected. This is +300%. If you can only affect one of the five basic senses and anything related to them (e.g. all hearing, sonar, ultrasonic, etc.) this costs +50% instead.
- Cybernetic: As per the enhancement for Mind Reading (p. B69).
- Damaging: Your illusions cause damage. Treat this as for Stigmata (Powers, p. 95), but damage is of an appropriate type and you must contend with DR just like a normal attack. You could, for example, “draw a pistol” and shoot a target – if you succeed the Quick Contest your target would take piercing damage equal to your margin of success. DR would affect this damage normally.
+50%. Duplication: You can only create an illusion of something, somewhere, or someone you’ve seen before. Keep a list of what you can duplicate! -30%. Fatigue Only: This requires Damaging or STigmata. Any damage you inflict is FP, not HP. -20%. Flawed: Your illusions are not quite right. Decide how (e.g., everything you create is in black and white). This gives an automatic +3 to disbelieve them. -5%. The GM may decide that this is a leveled advantage – if so, each level gives others a +3 to disbelieve them and is worth -5%/level.
- Limited Scope Illusions: Your illusions are specific. Price this as an Accessibility (Powers, p. 99). Notable examples include “Animals only” (-25%), “Weapons only” (-40%), and one specific thing (-80%); e.g., “Toyota Supras” or “Spanish Gold Doubloons.”
Mobile: As perthe normal enhancement (GURPS Basic Set, p. 107), except that it allows Move equal to your IQ/3 per level instead of just 1 Move per level.
Telekinesis and Illusion
Telekinesis can be purchased to make your illusions more solid or even cause damage. This requires a Link (+10% will due unless you wish to use Telekinesis for other things). This gives you a +4 on Quick Contests.
If your Telekinesis only works for Illusion this would be worth a -30% Accessibility. If your Telekinesis is limited to a ST appropriate for your level – this is worth another -20%. This allows your illusions to use real weapons if you provide them.
Example Build: Phantasm
- For 10 points you no longer need to concentrate to maintain an illusion, for 15 more points your illusory people seem real.
- For 75 points your damage ignores DR.
- For 75 points your illusion fools all senses your target has regardless of what they are.
- For 10 points your illusions last 10 seconds after you stop concentrating. Add 5 points to increase duration to 30 seconds, 10 points for 100 seconds, 15 points for 5 minutes, and so on.
- For 5 points your illusion can be up to 4 yards from you, for 10 points it can be 8 yards, 15 points it can be 16 yards, and so on.
- For 10 points you can project your illusions up to 100 yards from your current location.