Dragon’s Fire  
Dragons are naturally able to breath fire. It comes from the back of the dragon’s mouth. They creating it, by exhaling a flamable gas and flick their tongue on the back of their mouth.
 
Spike, being a magic infused dragon able to choose between two types of fire: Normal Fire and Magic Fire. The way he chooses between the two is how much force he puts into it. Magic Fire is a lighter breath compared to the normal one and he also needs to use his whole throat to use the magic in his body.
 
Normal Fire works just like any other dragon’s fire, it burns everything it touches.
 
Magic Fire in rare cases can cause small burns, but it doesn’t destroy. Spike’s magic fire gives him the ability to teleport items.
 
Dragon’s Smoke  
Dragons can exhale smoke (let’s call it “smoking”), that comes deeper from their throat. This can happen on it’s on, as it reacts to changes in their breathing. So it can react to their emotion, most of the time to anger. However, they can “smoke” when their body relax. So most dragons exhale smoke when they are sleeping. This can become a problem for other creatures, if the dragon decided to spend their hundred years sleep close by.
 
Dragons can choose to “smoke”, by heavily exhaling. Naturally the smoke only comes out through their mouth, but if they do it on purpose they can make to go trough their nose. Most of the time they use it for intimidation.
 
In Spike’s case, for the Magic Fire he needs to use the back of his troat, so his smokes always magic infused, but it’s weak magic, so it has no effect on anything.
 

 
Another head-canon, starring older Spike, Smolder and baby Ash.
 
Not really a deep one, but it’s something I wanted to write down for a long while now.