Intelligence is a word that is incredibly difficult to define, as it has been used to refer to many things, such as one's ability to process information, or their capacity for logic, self-awareness, creativity, reasoning, and/or problem solving, or their knowledge and memory. In its fullest definition, intelligence can be said to encompass all these things, which makes it incredibly difficult to quantify in versus debating terms, as many individuals may have plentiful ability in one area, such as knowledge, and also be lacking entirely in another, such as planning, emotional intelligence, or creativity.
As opposed to attempting to reliably quantify intelligence, pages should reflect that intelligence has many facets and, when describing the intelligence of characters, specifically detail their areas of strength while acknowledging any intellectual shortcomings they may have. Characters can be listed as having average knowledge overall while being geniuses in certain topics - Goku, for example, despite having little knowledge or skill in most other areas, is a martial artist of prodigal skill. This being said, the higher you go on this recommended scale, the less possible this becomes, as categories become broader and broader, with Supergenius itself implying overall brilliance surpassing that of human plausibility.
An intelligence quotient, or IQ is a scientific attempt to score the intelligence of individuals in real life through testing. It is a common occurrence in fiction for authors to give their characters IQ scores, often exceptionally high ones, and while some scientists believe IQ has validity in real life, it makes for a very poor measuring stick in fiction. An author can give a character as ridiculously high of an IQ as they want, whether it be over 200, 314, 5, 000, or even 10^30, but without feats, these numbers are meaningless, only acting as confirmation that they are much smarter than normal humans.
Even if that was not the case, as different fictions give their characters different ratings, they are completely useless for comparing intelligence between them. It would be like trying to compare the power levels in Nanatsu no Taizai to those in Dragon Ball to determine their power in relation to each other, when both verses use power levels differently and have completely different scales of power. This is without getting into the fact that many scientists find IQ to be a poor judge of intelligence for the same reasons that intelligence is so hard to quantify in versus debating, among others.
Some verses, such as DC Comics, have their own internal intelligence ranking systems. It is the same situation with these as it is with IQ - without feats, these rankings mean little.
There is no way to reliably quantify intelligence, and even these rankings are just suggestions and guidelines for pages. It is more important that a page discusses a character's intelligence and gives feats for their varying skills than have a solid ranking, though it may help with quickly summarizing their overall intellects and how they measure up to others.
Mindless: Those few beings that are literally mindless and have no capacity for intelligence at all.
Animalistic: Beings, such as animals, that only possess basic reasoning, awareness, and problem-solving skills. While various animals, such as chimpanzees, may possess higher capacities for such things, their intelligence would still remain animalistic.
Below Average: Characters of below average intellects and unremarkable skills.
Average: Characters of average intelligence. While they have more developed intelligence in certain subjects, in many cases, their overall intelligence remains average.
Above Average: Characters that show greater cognitive ability than the norm, but do not particularly stand out in any intellectual or academic fields.
Gifted: Character that demonstrate high reasoning ability, can master concepts with few repetitions, and display high performance capability in intellectual, creative, or specific academic fields.
Genius: Individuals with an exceptional capacity for knowledge and intelligence, generally in one area of varying depth, often possessed by fictional scientists and strategists. This level of intelligence is the level of actual geniuses and famous intellectuals in the real world and, in lieu of better feats, should be the default intelligence category for fictional characters treated as if they have exceptional or superhuman intelligence.
- Examples: L and Light Yagami (Death Note), Conan Edogawa (Detective Conan), Solid Snake (Metal Gear), Shikamaru Nara and Kakashi Hatake (Naruto), Colress (Pokémon), Sherlock Holmes (Sherlock Holmes), Kurama and Yū Kaitō (Yu Yu Hakusho)
Extraordinary Genius: Individuals whose knowledge spreads over many fields of science and who vastly surpass the intellects of the smartest humans on Earth. At this level, many are capable of creating futuristic technology, executing complex strategies even under high pressure, and potentially even accurately predicting the future through sheer mental calculations, or outperforming supercomputers. This is where super scientists of exceptional scientific knowledge begin to appear.
- Examples: Kisuke Urahara and Sosuke Aizen (Bleach), Lelouch vi Britannia (Code Geass), Batman (DC Comics), Bulma, Doctor Gero, and Android 21 (Dragon Ball), Spider-Man, Bruce Banner, and Iron Man (Marvel Comics), Dust of Osiris (Melty Blood), Accelerator (To Aru Majutsu No Index), Ozymandias (Watchmen)
Supergenius: The highest level of non-omniscient intellect, possessed by those individuals with unfathomably superhuman intelligence and usually extensive mastery of most, or all, branches of science. Characters of such a scale tend to be super scientists capable of creating impossibly advanced physics-defying and reality-warping fantasy technology even with just household items, and outsmarting even other extremely intelligent individuals. Supergeniuses can often easily process calculations beyond modern humanity's combined capabilities on their own, and quickly come up with extremely complex plans.
- Examples: Professor Paradox (Ben 10), Brainiac (DC Comics), The Doctor (Doctor Who), Doctor Doom, Mister Fantastic, Thanos, and the High Evolutionary (Marvel Comics), Rick Sanchez (Rick & Morty), Washu Hakubi (Tenchi Muyo!), Lum (Urusei Yatsura), The Emperor of Mankind (Warhammer 40,000)
Nigh-Omniscient: Characters who have knowledge of nearly everything, with only minuscule gaps existing in their knowledge.
- Examples: Doc Scratch (Homestuck), Eternity and other abstracts (Marvel Comics), Arceus (Pokémon), Q (Star Trek), Featherine Augustus Aurora (Umineko no Naku Koro ni)
Omniscient: Characters who know literally everything. Be aware that even if they may know everything in their own setting that this does not grant them knowledge of beings from outside of it.