Basically, this is a rankings system. There are finer degrees than this system allows for, but since most of the characters are metahumans, chances are they fall above human ranges more often than not. Until I get more data, most of the examples will include actual comics characters, as opposed to Retcon characters.
STRENGTH: one of the more common super powers, metahumans tend to display strength beyond what someone of their height and build should possess. Most of the Retcon heroes will still fall into human ranges; at her 'default' height, Giganta falls well short of human maximum strength, but still a lot stronger than she ought to be.
Class 0: Basically, you have a non-ability. You can't exert any force on your environment. Example: The Brain (DC)
Class 1: Low end of human ability. Maximum press over your head about 40 lbs.. Good range for children and the elderly. Example: Aunt May (Marvel)
Class 2: The so-called 'average' strength. Maximum press up to 100 lbs.. Example: Lynceus (Real Life)
Class 3: Above average strength. Maximum press up to 400 lbs.. Example: Robin (DC)
Class 4: Extreme human strength. Maximum press up to 800 lbs.. Example: Captain America (Marvel)
Class 5: Mild Superhuman strength. Maximum press up to 1.5 tons. Example: Beast (Marvel)
Class 6: Incredible strength. Maximum press up to 10 tons. Example: Spider-Man (Marvel)
Class 7: Ridiculous strength. Giganta at her maximum height falls in here, I think. The force a Green Lantern Power Ring can exert would be here as well. For obvious reasons, we shouldn't have too many heroes in this range.
AGILITY: This covers all forms of physical coordination, balance, grace, athleticism and the like. Which may not be realistic, but it gives you a range.
Class 0: Non-ability. You can't move. Example: Stone Boy (DC)
Class 1: Total clutz. Example: ?
Class 2: Average Joes. Example: ?
Class 3: Above average agility. Example: Kick-Ass (Marvel)
Class 4: Olympic-level athlete. Example: Black Widow (Marvel)
Class 5: Enhanced Ability. Not going past this, because really, most examples of grace and agility beyond this point are the result of powers, not raw ability. Example: Nightcrawler (Marvel)
ENDURANCE: Staying power, the ability to overcome pain, fatigue, and injury. Characters with high endurance simply don't give up, even when they're very badly hurt.
Class 0: You don't have any real biology to speak of. Before you think this is a good stat for undead or robots, note that those kinds of characters have their own form of staying power, be it a battery or an animating force.
Class 1: Very feeble constitution. Winded by normal activity. Example: ?
Class 2: Normal human range, you get winded by walking up a few flights of stairs. Example: ?
Class 3: You engage in regular exercise. Example: Batgirl (DC)
Class 4: You engage in intensive exercise, and are no doubt a profesisional athlete. Example: Punisher (Marvel)
Class 5: Enhanced ability; your body can withstand brutal extremes of punishment and exhaustion, and still recover after rest. Example: Marv (Sin City)
Class 6: Jason Voorhees ain't got nothing on you, short of killing you outright, nothing can stop you! Example: Juggernaut (Marvel)
INTELLIGENCE: The standard IQ scale should work for most characters; while metahumans can have exceptional gifts of recall, ingenuity, and processing data, I highly doubt any character will have an IQ beyond the normal current human record (210 IQ). Some of the most brilliant people in history fall well short of that lofty mark, after all. AFAIK, the Luthors are canonically the smartest characters.
This isn't to say that there aren't metahuman abilities that simulate ridiculous intellect; Cat-Woman's Gadgeteer trait, for example.
WILLPOWER: The mental equivalent of Stamina, and closely related in many respects. The mind can overcome the body's weakness, to some extent. Heroes often have tons of Willpower, making them brave and able to keep on fighting. However, just because you have great will doesn't mean you don't have the occasional breakdown. It's your ability to recover from psychological trauma that determines your will, not simply your resistance to it. Most of our characters have oodles of Willpower by definition, as they have to overcome and deal with drastic life-changes. Psychic abilities, Magic, and, of course, Green Power Rings are more effective when wielded by characters with extreme Will. People with high Willpower tend to be charismatic individuals, who draw others to them with the sheer strength of their personality.
Class 0: You exist, and that's about it. Example: ?
Class 1: You are gullible, easily tricked or fooled, and flee or become paralyzed with fear when in danger. Example: ?
Class 2: Normal human. You can be stubborn, but rarely stand out. Example: ?
Class 3: Perhaps you're a natural leader, or you don't take guff from anyone. You have a will stronger than most. Example: Purgatori (Retcon)
Class 4: You have faced considerable trauma in your life, but you endure, as you always have, and have the courage to do what must be done. Example: John Hartigan (Sin City)
Class 5: Epic willpower. You have faced your fears, and overcome them. Now you stand as a shining beacon, a rock that others can count on always. Example: Jade (Retcon)
SKILLS: The next category is fairly obvious; each character has a number of different skills. For ease of use, we can rate these as follows:
0: You saw it done on TV once. 1: Basic to Junior High level knowledge. 2: Intermediate to High School level knowledge. 3: Professional to College level knowledge. 4: Advanced level; post-graduate studies, law or medical school. 5: Bleeding Edge. 6: You have experience in your field greater than can be gained in a human lifetime.*
- Powers can let you function at this level as well, a good example would be Gadgeteers like Forge (Marvel) or Cat-Woman (Retcon), who can build things that others cannot.
It's not necessary to rate every skill your character has, of course. Most normal people have 1's and 2's all over the place. Our heroes and villains have quite a few 3's, and no doubt higher skills.
Some examples of this in action:
Dr. Doris Zeul has a doctorate in Genetics. We could say she has a level 4 in this field. Dr. Dabney Donovan, on the other hand, has been working with genetics for decades, and, assuming he hasn't become incapable of learning from modern advances, would likely be a level 5.
American Dream has been a soldier most of her adult life. Her knowledge of Martial Arts, Firearms, and Melee Weaponry is easily at level 4, possibly even 5!
(An immortal, like, say, Thor, might have Melee Weaponry skills at 6, if they continued to incorporate new techniques into their fighting style. Then again, how much finesse does one need to swing a hammer anyways?)
Skill rankings should only come up when two characters interact; if your skill is two levels higher than someone else's, they can contribute little, and are likely outclassed. If you are only one level higher, however, there is a possibility you can be challenged. For example, let's take Dr. Zeul vs. Dr. Donovan.
At first glance, Dr. Donovan has the edge here. He has more experience, and may very well be smarter! However, Doris worked closely with Professor Zhan, who was more knowledgeable, and together they developed the Herakles formula that was the basis for the metagene activation technology Lex Luthor acquired. Thus, when it comes to the subject of Metahumans, Giganta may have an edge.
Green Lantern II and Terra are both huge comics fans, knowing obscure details people who have read comics for years would be amazed (or disturbed) to know. Let's assume they both have Geek Lore-Comics at level 4. Terra is older, however, and has had a few extra years to soak up data about comics history, and she's definitely the expert on Power Girl and, well, the new Terra, so she wins debates in these areas more often than not.
TALENTS: These are those minor things that set you above other humans. It can be a knack for a Skill, being ambidextrous or having eidetic memory. Since these are traits normal people have, they're not really powers, per se. There is a little bit of overlap, especially when dealing with low-level psychics or occultists.
POWERS: More on this later; I won't make an exhaustive list of powers (others have done that). What is needed is a good way to rate ability. For example, Wolverine has feral senses. Martian Manhunter has seven senses (at least!). So, of the two, who can gain more data from their environment?
Flight. In my own stories, I've established the following: Purgatori > Alena > Jade. Jade is probably the current King (er, Queen?) of Flight. I would imagine Magik is roughly equal to Alena in flight ability.
We can assign ranks to individual powers, but that only helps when pitting one power directly against another. For example, Alena is very good at phasing (“into the Fourth Dimension”, according to the Star Heart). Jade may or may not have the same ability, but when she first encountered Alena, she wasn't aware of it. So she instead used her Power Ring to generate radiation that countered Alena's phasing abilities temporarily.
Giganta can increase her density to an unspecified degree; the larger she grows, the stronger this ability gets. Thus, she can be incredibly hard to hurt, and is quite stable. But what if Terra tried to use her geokinetic powers to trip the mighty giantess? Or Phoenix attempted to move her with TK?
This sort of power vs. power interaction will be common in stories, and a simple rank vs. rank comparison could be useless. Like the traditional Wizard's duel, the more creative mind will likely win out in the end.
Powers do not replace your brain!
RESILIENCE: This power is almost a talent for metahumans, as almost every metahuman has some degree of increased resistance to injury. This is from a combination of altered body structure and/or density. This trait differs from traditional invulnerability in that, you are still hurt, even if you have high resilience. Your body shows injury and damage. You simply can take a much larger beating than you have any right to.
Note that, even though they may not be technically metahumans, Green Lanterns seem to gain this ability as well. It's established in comics canon that the Power Rings do not automatically protect their wearers; if you want a force field or armor, you have to actively generate it.
Which leads me to a tangent about the Power Rings and armor. Using Jade as our example, her uniform, though it looks and feels like Lycra, has minor defensive abilities; roughly equal to say, thick leathers. It's also climate-controlled.
The minor rings that Jade has given to Earth's new heroes, however, only generate illusions. Thus, they cannot provide armor in any way, shape, or form. If for some reason a shirt became separated from the body more than a few inches, it would fade away, but has mass when worn, much like Tori's (Human) or Terra's(male) alternate identity skin. In other words, when Terra presents as a boy, you can feel her hair, she's taller and solid in the trunk area, etc.
The clothing can be 'damaged' as well, but it takes only a moment to 'repair' or replace your costume. For characters like Giganta, all of this means that she is basically naked whenever she uses her powers, although it looks and feels like she's wearing clothing, even though it's just an advanced illusion.