How can I apply an illness during character creation? I'm thinking of a character that has leukemia that its effects can happen during the game and provoke some negative modifiers to all tests (due to internal bleeding and nausea, I'm thinking on a -4 modifier) while the disease effects manifest.
Since this is 2E, you can also make use of Drawbacks. This could be modeled using Vulnerable (which does indeed increase difficulty of certain saves), Weakness (which progressively reduces your stats under certain conditions, such as not getting your medicine), and Disability (more of a general reduction in checks, or inability, due to physical or mental ailments). As with all aspects of the game, it will require working with your GM for what the Frequency and Severity of the Drawback is, but you'll get some additional points to spend on your character.
You’re vulnerable to a particular type of attack. Frequency is based on how often you encounter your vulnerability. Intensity measures how vulnerable you are; minor vulnerabilities add +1 to saving throw DC. Moderate vulnerabilities increase the modifier to the save DC by 50% (× 1.5, round up). Major vulnerabilities increase the save DC modifier by 100% (× 2). So, for example, an attack doing +7 damage normally does +8 damage to someone with a minor vulnerability (7+1), +11 to someone with a moderate vulnerability (7 × 1.5 = 10.5, rounded up), and +14 to someone with a major vulnerability (7 × 2).
You suffer harm from something normally harmless to others. It may be a vampire’s weakness to sunlight or holy water or a hero’s weakness when exposed to glowing meteorites. Alternately it may be the lack of something, like a vampire’s need for blood, an addict’s need for a drug, an amphibian’s need for water, and so forth. Frequency is based on how often you encounter your weakness. Intensity is based on the effect the weakness has on you.
- Minor: cumulative –1 on checks, attack bonus, or defense bonus.
- Moderate: cumulative –1 penalty to all checks, attack rolls, and Defense, or a –1 cumulative drain on an ability score.
- Major: cumulative –1 drain on all ability scores.
The base time before a weakness affects you is 20 minutes. Increase the drawback’s value by 1 for each step up the Time and Value Progression Table and decrease it by 1 for each step down. So a weakness that affects you each round is +4 points while one that only affects you once a day is –3 points. If your weakness is an Instant rather than a continuing effect, like an attack, it has a time modifier of +0. If your weakness affects your Constitution score (and therefore might kill you) add +1 to its value.
You lack a particular ability most people have. The frequency of the drawback is based on how often this lack limits you, while the intensity represents how serious a limitation it is. Some examples include blindness (very common, major, 5 points), deafness (very common, moderate, 4 points), one arm (very common, moderate, 4 points), mute (very common, moderate, 4 points), paraplegic (common, major, 4 points), one eye (–4 with ranged attacks, common, moderate, 3 points), and illiterate (uncommon, minor, 1 point)
The complication rules (page 122, Mutants & Masterminds second edition) cover conditions intrinsic the the character that can arise during game play.
Several example complications can fit the life-impact of a terminal disease.
- Accident caused by symptoms flaring up during stress.
- Addiction to painkillers and other symptom management drugs.
- Fame as a patient struggling with disease and fighting super crime.
- Prejudice as a sick person or "disease vector".
- Secret illness and the struggles to conceal it from the world.
Further, the listed complications are non-exclusive ("Possible complications ... include:" is a non-exclusive statement). A Symptoms Flare complication, that awards a Hero Point but inflicts a -4 penalty to attack, skill, and attribute checks for the scene, is probably reasonable. Make sure to get it approved by your game master.
Per chapter 3, Abilities, you can start with ability scores below zero, but not below -5.
When I was designing a bed-ridden psychic (inspired by Vampire Hunter D…), I simply used -5 strength and -5 stamina. Depending how severe you feel your leukemia would be, you could adjust those values.
If you want leukemia to be a constant character trait but not a constant hindrance, consider buying your traits back to zero with the Enhanced Ability power — this almost always works the same as being normally-healthy, but disables you if your power is nullified.