There is unfortunately no purely mathematical way to create a balanced power. Many factors have to be taken into account. Here are the guidelines that we used to create the super powers to begin with. If you or your GM want to invent a new one, follow these general guides and use your judgement. Be prepared to change the power after you’ve designed it and even used it in a game or two. If it seems to powerful in the game, then reign it in. If it seems useless, then beef it up.
Don’t Duplicate a Power
The first question to ask yourself is if the power you want to create is already in the system. For example, there is no power called Claws because the Natural Weapons trait already does that. There is not Heat Vision because Energy Attack already does that. Similarly, there are powers you can get only by combination, which is on purpose. The powers do only what they say they can do. If you want a useful ability out of the game, you have to pay for it. The argument that, “with this power I should be able to do something else” is anathema to the philosophy of this system.
By keeping the powers as separate as possible, the system provides both a great deal of flexibility and maintains fairness. In this system, you cannot for example take Fire Form and thus gain flight, flame strikes, heat resistance, etc. If you want to build a character with all those abilities, you have to pay for them individually. Making a power that simply combines several powers that are already in the game essentially breaks the system as it’s designed, so don’t do that.
Look for Pre-Existing Versions
The second question to ask is whether the ability you want is already in the SRDs somewhere. If it is, then you can probably cut and paste those rules, with a little tailoring. If the power you want is a spell, for example, you’ll probably have an easier time designing it than if you’re making it up from scratch.
Determine CP Cost
Add all of the following up in order to get a rough estimate of a power’s cost in CPs. Mêlée damage is reckoned at about 1CP per 1d6. A 30-foot Touch attack costs on average about 3CP. A range increment of 50 feet costs 2CP. There are many standardised prices for enhancements, like activation time increases and decreases (2CP per action), as well as reflexive shifts (3CP). Look through the enhancements to get an idea of what already has a price and use it if it’s there.
One full power is about 8 to 10CP. By a “full” power, we mean that it has some kind of debilitating effect in combat (damage, unconsciousness, etc.), or it achieves some useful effect either in or out of combat (avoiding obstacles, manipulating objects in a convenient way, etc.), and it has a couple of useful enhancements loaded on to it. This is a very rough estimate, of course. The base powers are often about 5CP to start and then have options that raise the price further, but the more useful a power is, the more expensive you should make it. That point bears repeating: the measure of power’s CP cost is its use value in the game, not how hard it “should be” to achieve a certain effect by the reckoning of real-world physics or some such rationale. For example, flying at the speed of light is only 2CP because it’s just not that useful in a game.
Aside from sheer power level, flexibility is something else to take into account when pricing a power. A power that grants a specific bonus, a +2 to Defence for example, may be extremely useful but it’s limited to that one thing. A power that the player can shape into many and various forms should be very expensive, like Force Field. The moment you put that kind of creativity in the player’s hands, they will make something deadly out of it. This is not bad. Creativity is the soul of role-playing games. It just needs to be expensive.
Determine Power-Point Cost
Power Point cost is usually just 1PP to activate and 1PP per round to sustain, but if the power grants an especially useful ability, feel free to raise it, but keep in mind that a 4th-level character, the default starting level of the game, will have only around 25 PPs, on average. It’s perfectly reasonable that they can maintain a very strong power for only a few rounds. If the PP cost is 4PP per round, they will get only five or six rounds out of it before they need to rest and regenerate power points, and it’ll be the only power they can use.
Powers that are based on a unit of damage, healing, distance, weight, or the like and that you intend to be used regularly can be “By Character Level” (“By CL”). The exemplar for this activation cost is Energy Attack. Energy Attacks that do relatively little damage don’t cost anything in order to allow you to use them a lot. Very powerful Energy Attacks do cost a lot.
Determine Activation/Sustain Times
Finally, activation and sustain times are somewhat standardised. Movement powers should require no PP cost. Skill enhancers should require no cost. Powers/effects that inflict damage or heal damage should have a cost By CL.
The activation time can be a standard action if you think someone should be able to use the power and attack in the same round, or a move action if you don’t. Use a full-round action if the power ought to require a little more prep time and be a little less common in a fight. Sustainable powers should have a sustain time of “round/minute” or even “round/hour” if they’re useful outside of fights, but only for tasks that require time. For example, Size Shift can be very useful outside of a fight, but only if you don’t have to pay for it per round.
The sustain cost, if applicable, is just the activation cost and a free action, unless you think that sustaining the power should require attention, in which case assign a swift, move, standard, or full-round action as you see fit.
That’s about as specific as we can get with these guidelines. There is no formula to plug in and get a perfectly balanced power. You have to test it to know how it will behave in a game and you have to be willing to alter it once you’ve tested it to make sure that it works and is fair. If, as a GM, you do find that something is either too powerful or not powerful enough, you should just talk to the player and tweak it until it’s not unbalancing the game any more. If, as a player, you realise that it’s underpowered, then you have every right to ask if you can make it more on-par with your fellow players’ abilities. If you realise it’s overpowered, then it is your responsibility to suggest a way to limit it without ruining your fun. The best way to solve these kinds of problems is almost always the direct approach, person to person, rather than trying to solve it all in-character.