Illusion
Under the Hood: Illusion
Illusion is a broad-ranging effect, usable for a number of different things. A few common considerations for Illusion include the following.
Damaging Illusions
For illusions so realistic they are capable of inflicting damage, add a Linked Perception Range Damage effect. At the GM's discretion, this effect can even be made into a Linked Array with a variety of alternate attack effects, allowing your illusionist to inflict conditions other than damage on targets. Keep in mind the attack effects all need to be perception range to match the range of Illusion.
Illusory Appearance
Illusion can alter a subject's appearance, providing an essentially impenetrable disguise--at least until someone makes a successful check to see through the illusion. However, for just the ability to alter appearance, use the Morph effect, which is generally more effective than Illusion Limited to Appearance.
Mental Illusions
The default Illusion effect is perceptible to anyone or anything (including machines) as if it were real. Some illusions exist solely in the mind, like projected psychic hallucinations. This is only a descriptor and has no impact since you must still choose which senses the hallucination can mimic. This type of Illusion is typically has the Resistible by Will flaw and the Selective extra, for a net +0 modifier, however those modifiers are not required. This is not to be confused with illusions that trick mental senses. Illusions can't trick memories etc for that see Mental Transform.
My Ally, My Enemy
A common Illusion trick is to switch the appearances of an enemy and an ally, causing a foe's teammate to attack that enemy by mistake. You can generally handle this with an opposed check of Illusion and Will; if you win, the target is unaware of the switch and attacks the wrong target.
I Disbelieve!
Keep in mind characters don't get to make a defense check to overcome an illusion unless they have reason to believe the illusion is not real. Given the rather fantastic things that can happen in different settings, an illusion generally has to provide some evidence of its true nature. Smart illusionists keep the true nature of their powers secret, and smart Gamemasters require players to come up with something a bit more comprehensive than "I disbelieve!" to figure out when there are illusions at hand.
You can control others' senses to create false impressions, illusions. This can range from visual images to phantom sounds, smells, or even radar or mental images. For 1 point per rank, you can create an illusion affecting a single sense type. For 2 points per rank, you can affect two sense types. For 3 points per rank, you can affect three sense types. For 4 points per rank, you can affect four sense types, and for 5 points per rank, you can affect all sense types. Visual senses count as two sense types. Your rank determines how convincing your illusion is, that is to say, the DC for the Will defense or Insight check is equal to your rank.
Illusion Size
Your illusion occupies an area with a maximum volume rank equal to your effect rank. To increase the size of the illusion you can create, apply the Area extra; each application increases the area your illusion covers by 1 rank.
Illusionary Effects
Illusions have no substance and cannot have any real-world effect. So they cannot provide illumination, nutrition, warmth, or the like (although they can provide the sensations of these things). Likewise, an illusory wall only prevents people from moving through an area so long as they believe it's real, and an illusory bridge or floor is revealed as false as soon as someone tries to walk across it, and falls through it!
Detecting Illusions
Characters encountering an illusion do not receive checks to recognize it as illusory until they interact with it in some fashion. A character may perform an Insight check against an illusion (DC equal to Illusion rank), a success reveals it as false. A failed check means the character does not notice anything amiss. Senses with the Counters Illusion effect automatically detect illusions. Circumstances may grant bonuses to the check to uncover an illusion, depending on how convincing it is. Note that even if you are certain what you perceive is an illusion, it won't go away until you can pass a Will defense check.
Overcoming Illusions
Whenever a character finds evidence that the illusion isn't real, such as being told that it isn't real, a check can be made to overcome it. A successful Will defense check (DC equal to Illusion rank) will overcome the illusion making you unable to sense it further. Senses with the Counters Illusion effect on the other hand can still detect illusions that have been overcome.
Maintaining Illusions
A static illusion or one in a fixed loop can continue without needing commands from you. However if you'd like your illusion to react to circumstances it will require an additional free action from you per round. For example if you have a Continuous Illusion of a man evading your victim and you fail to take a free action to control how it should move then it will still exist but will stop moving. Likewise illusions are limited by your imagination: if you don't know how it should look or how it should act then you'll have to guess if you want it to exist at all.
Extras
Independent: Your active illusions only require a free action to maintain, rather than a standard action. +1 cost per rank.
Selective: You choose who perceives your Illusion and who doesn't. +1 cost per rank.
Flaws
Feedback: Although Illusion does not have a physical "manifestation" per se, it can apply this flaw, in which case a successful damaging attack on one of your illusions causes you to suffer damage, using the guidelines given in the description of the Feedback flaw. -1 cost per rank.
Limited to One Subject: Only a single subject at a time can perceive your Illusion. -1 cost per rank.
Reduced Range: It is left to the Gamemaster's discretion whether or not Illusion's range can be reduced at all, since using an attack check to affect everyone who can perceive it is odd (even more so for close range). In order to solely alter your own appearance, see the Morph effect, possibly with the Resistible modifier. -1 cost per rank.
Resistible: Illusions Resistible by Will are typically hallucinatory effects projected into the target's mind. This flaw is commonly combined with Selective, so only the targets you choose perceive your illusions. Illusions Resistible by Fortitude may represent a hallucinatory drug or similar biochemical effect. This defense check is done when first perceiving the illusion to determine if the target can resist the effect entirely. If successfully resisted that character remains immune for the entire illusion duration except under certain circumstances determined by the Gamemaster such as leaving the area and returning. -1 cost per rank.