Smokecrafters (I’ll use that name for now. Sounds good haha) would have a genetic affinity for smoke manipulation. I was thinking about 1 in 20 people would have it. Still, in order to practice the magic well and safely, users go through intense training. This takes time, so fully trained smokecrafters would almost always be adults. What spells they know would heavily depend on the environment, as not every area would have the same materials to burn. At least, not have them in great supply. In larger cities, this would be less of a problem because many of the herbs, materials, etc. would be imported.

Most of the time, burning one item is not enough. It takes a combination of various materials to achieve an effect. For example, if a smokecrafter wanted to speak to the dead, they would first, need to gather their bones. One bone could do the trick, but the more bones the better. It is nearly impossible to fully burn human bones, especially with a normal fire. A smokecrafter would need to burn the bones along with herbs that generate hallucinations, images, and alter perception of sound and understanding. Once the bones are charred, however, they no longer have their summoning abilities.

All of the burning is time sensitive. Once the source is used up, it can’t be used again.

Not everything that can be burned is worth the effort. Most leaves, for example, dont generate enough smoke to do anything with. Leaves can be used as a supplement in some cases when needed. An important thing taught to smokecrafter apprentices is what materials native to their regions have greater effect and which don’t.

I would have to figure out what materials would work. I have some ideas, but nothing specific:

Poison ivy = an irritant; probably causes coughing

Animal bones = conjure illusions of or related to that animal; can be combined

Hallucinogens = inhaled by smokecrafter or used on others for various effects

Types of oils = help keep the fire going, but can lessen the power

Thats all I’ve got for now :)