4: Design the Game Mechanics – Disadvantages and Skills
Disadvantages are the opposite of advantages, at least in theory. In practice they are the opposite in one way - they give the character a penalty where an advantage gives them a boost, but serve the same function when it comes to distinguishing the character. After all, being an insufferable know it all is clearly a disadvantage, but it does serve to neatly spotlight Ms. Granger's character.
At creation a character has at least one disadvantage, and possibly more if she also has additional advantages. It is very possible, indeed probable, to gain or lose disadvantages in play. Hogwarts is a place of growth and self-discovery, and that means overcoming one's perceived limitations - and possibly creating new ones in the form of enemies or curses! Many of the following disadvantages are meant to be overcome in play.
Suppressed Quality: one of the character's qualities is artificially reduced by 2 points for tests - they possess the base quality, but are not comfortable enough with it to use it to its full advantage. There are common names for this: Bravery is suppressed by Insecurity (Neville Longbottom starts with this but overcomes it); those with weakened Ambition are Artless (Hermione begins with this, but loses it over time); a suppressed Intellect makes the character Scattered (Luna Lovejoy never loses this) and Fortitude is suppressed by Weakness. The character still has a strong statistic for the sorting hat to detect, but until she overcomes the disadvantage all tests made with the quality are at the lower level except in extreme circumstances as determined by the GM.
Small: The character is tiny, with little chance of getting bigger. The characters size is reduced by 1 point to a minimum of 1, and annual rolls made to increase Size are made at a +7. It is possible to take this twice, and the character is likely a Half Breed, but it is not a requirement. Professor Flitwick has this disadvantage.
Over-focused: the character's worst quality is reduced by 1 point, to a minimum of 1. If her worst quality is already a 1, the next highest stat is reduced.
Orphan: The character has no one to turn to and nowhere to go. While still a child she is entirely dependent on the good will of others, and even that is stretched to the point of being intolerable. In addition to lacking familial support the GM can apply a 3 point penalty to any test where the character's orphaned state could apply. Harry Potter has this disadvantage.
Poor: The character's family is not well off, and therefore everything she gets is well used to the point of being worn out. In addition to lacking liquidity the GM can apply a 3 point penalty to any test where the character's equipment might fail her.
Famous: The character has the worst sort of fame - the sort where she gets no privacy, is always under the microscope and is chastised by adults for failing to set a better example (or, if notorious, for not being better than she is). It is possible to have the disadvantage of Fame with none of the advantages. There are no mechanical aspects to negative fame - they are entirely situational - but that makes them no easier to live with.
Magical Ineptitude: The character is particularly bad at one form of magic required by the school. Any tests made with that magic skill are at a -6 penalty This might be a family curse or just a quirk of the character. You can pick the skill or let the GM roll to preserve the suspense.
Common Failure: The character is notably unskilled with a common skill, suffering a -3 all tests using it. This must be one of the listed Common Skills and not a 'wild card' skill - being notably unskilled with gambling or music isn't enough of a disadvantage, but being bad at mischief or athletics is. You can pick the skill or let the GM roll randomly to surprise you at just the wrong moment with your sudden incompetence.
Unflattering Feature: the character is plain, with a single feature that pushes them into being noticeably unattractive. She suffers a 3 point penalty on any test where physical attractiveness plays a major role. This can be taken twice, meaning all of the character's features are unflattering and she is downright ugly. Hermione Granger started with this disadvantage - her teeth - but lost it in book 3.
Klutz: In moments of stress the character's qualities fail to save him from his lack of grace. You can only take this disadvantage if your character's Agility is lower than at least two of your qualities, and it means that she can never default to a higher quality regardless of the circumstances.
Professor Enmity: One of the professors just hates the character, and will go out of his way to make her life difficult. We can engineer a reason for this during the character's first days at the school or she might never learn why one of the teachers hates her. You should clear this disadvantage with your fellow students, as it has a "spillover effect" onto your character's friends. Harry Potter has this disadvantage concerning Snape.
Enemy: The character has someone who hates her and wishes her ill, perhaps to the point of killing her. The power of the enemy is balanced by their frequency - someone who turns up rarely will be more powerful than someone who is making her life miserable all the time. Particularly powerful and well connected enemies are worth 2 disadvantages. You should clear this disadvantage with your fellow students, as it has a "spillover effect" onto your character's friends. Harry Potter has this disadvantage three: Draco Malfoy and Lord Voldemort, who counts for double.
Half Breed: The character is only part human, but can generally pass for an extreme example of humanity. This carries with it some severe social penalties if it becomes known. The character originally has to worry about keeping this a secret (which the GM will contrive to make difficult) and if it comes out suffers a -3 on all social test from that point forward. You can abandon the idea of keeping it secret and start as a known half breed, or a full blooded non-human, such as a centaur, with the social penalty.
Player Defined: as with Advantages, these standard disadvantages are meant as examples and can be added upon if you develop unique for your character.
Skills, unlike qualities, are the thing the character can learn and improve in - acquiring skills is why they are students, after all! Skills fall into three categories: Magical, meaning that they are things only witches and wizards can do: Common, things that anyone can do regardless of magical status; and Muggle, things that are directly tied to technology. Obviously, the last group is of the least importance in the game.
As noted above, first year students have 15 points to spend on skills, with Purebloods able to spend up to 6 points in magic skills but none in Muggle skills. Half Bloods can spend up to 3 points in both Magic and Muggle skills and Muggles can spend up to 6 points in Muggle skills but none in magic skills. This is not a lot of points, but as first year students the characters are not very experienced. They will get better over time.
General Muggle Skills
A note on Muggle skills: this game takes place 9 years before Harry Potter's arrival at the school in 1991. It is 1982, and you should set your tech expectations to that era - no internet, few home computers, no cell phones. Functionally, it's the dark ages.
Muggle Medicine: the character knows Muggle first aid and, at higher levels, specific types of medicine like dentistry & pharmacy. First aid can be useful in the wizarding world if no magical healing is available.
Muggle Mischief: This skill lets the character pick locks and otherwise evade security. It only works on Muggle precautions but require no magic to use.
Muggle Science: The character knows one or more Muggle sciences (other than medicine). This has limited utility at Hogwarts. Each 3 points in the skill adds another science to those she can understand.
Muggle Sports: The character is versed in non-magical sports like "football" & "cricket". She can bore wizards with the rules & history of these games and display physical skill with them if called upon.
Muggle Studies: the character knows how Muggles live, how their money works, how to use a telephone, how to navigate cities without the use of magic and other potentially useful skills. This is also taught as a class at Hogwarts, but Muggles come by it naturally.
Muggle Technology: The character knows how to operate some advanced Muggle tech, like a computer, car, sound board or similar apparatus. Each 3 points in the skill adds another piece of tech to those she can use.
Muggle Wild Card: The character has some other Muggle skill, player defined with support from the GM.
General Magical Skills
Astronomy: On the surface this is equivalent to the Muggle science of the same name. Astronomy is also the science of tuning magic to avoid deleterious effects from planetary and stellar alignments, and is key in the creation of and experimentation with new spells.
Broomstick: The character's skill with the standard form of wizardly locomotion.
Charms: A type of magic concerned with giving an object new and unexpected properties
Defense Against Dark Arts: This class teaches defensive techniques to block spells, charms, curses, hexes and jinxes cast by other wizards, counteract the Dark Arts, and to protect from Dark creatures.
Herbology: The study of magical plants and how to take care of, utilize and/or combat them.
Magic History: This doesn't actually require magical knowledge, but it is only know by the wizarding peoples, and is lumped here. It is the history of the wizarding world
Potions: The art of creating mixtures with magical effects. It requires few incantations, instead requiring the correct mixing and stirring of ingredients at the right times and temperatures.
Transfiguration: The act of changing something into something else through magic.
Wizard Culture: The wizard equivalent of Muggle studies, it's the things everyone knows, from how to use Flue powder to the rules and lore of Quidditch.
Ancient Runes; an advanced class, it is not something known to first year students. Runes are used most often in the creation of magical artifacts.
Arithmancy: an advanced class, it is not something known to first year students. As the study of magical numbers it is useful in handling either exceedingly large or small amounts of magical energy in a spell, and in preparing formula and rituals for those spells.
Divination: an advanced class, it is not something known to first year students. It is the act of using either magic or magically guided observation of natural events (such a the pattern or tea leaves or the flights of birds) to tell the future.
Magical Creatures: an advanced class, it is more often known to first year students than similar classes. It is both theoretical and practical knowledge of magical creatures that inhabit the world.
Magic Wild Card: The character has some other magical skill, it's player defined with GM support.