After years of continuous smoking, you’re addicted to nicotine and always have cigarettes on you. Your lungs have sustained permanent damage, but there are a couple benefits.
Your lungs have received permanent damage, slightly weakening you:
Your constitution score decreases by 1, your walking speed decreases by 5 feet, and you have disadvantage on athletics and acrobatics checks.
Then, two other ability scores increase by 1. (One of these scores cannot be constitution)
You’ve learned to use your lit cigarettes to harm. Starting at level 3, you can perform a special unarmed strike, except it deals fire damage, and its damage is a d4.
You can instill a coughing fit in yourself, coughing and hacking up large amounts of smoke. Starting at level 3, you can cast the Fog Cloud spell, except it appears as smoke, not fog. Once you use this feature, you gain one level of exhaustion, and you can’t use it again until you finish a long rest.