I am looking for a way to make fire as an edible decoration. Looking for somewhat-realistic look to it.
I can't say I know anything about it, but I think you would get the most realistic look with pulled sugar.
3D or flat? You can do fire out of gumpaste or fondant. I have kind of a bad example of fire on my Harley cake if you're looking for flat. Or you could just color your buttercream orange and red (or airbrush if you have) and pipe it in a big pile like fire would look.
I did use the 2 tone bc on the piping bag,or maybe you can do some marbleling fondant using orange and red,there's even a template of the fire flames here on the gallery!
You could try colored chocolate and cut into flames. Maybe even comb the chocolate.
If you look at the cover of Hot Cakes she has fire going around her cake. she did this by rolling out a strip of fondant and then cutting half circles and making it look like fire here is a pic
I don't know if the cake is in my photos here, I think it is, I colored fondant and swirled it together then cut flames. If I had to do it again I would go online and get some better looking flames. It's not hard really, just get your colors right and cut away. You can make a flame template if need be.
I checked it's on page 4 of my photos.
Melt red, orange and yellow Jolly Ranchers, or similar hard candy, on a foil-covered cookie sheet, letting the colors swirl together. Let cool and then break into jagged flame shapes. Stick the base of each "flame" into whatever on your cake is supposed to be burning and arrange the pieces at different angles. It ends up looking pretty realistic.
I cut out fondant with my large and medium size leaf cutters. I then painted the leaves with food coloring. The larger leaf orange and the smaller one yellow and put them together. It gave the flame a grainy look but from the distance it looked really cool. I would post a picture but for some reason none of my pictures will post to CC.
Using buttercream: use a tip 21 in red with a fat "bottom" then pull up to make a point. Then use a tip 16 with yellow and do an overlay on the red. It will make a perfect flame.
As Holly above said I would use red/yellow/orange barley sugars or similar hard candy and melt in the oven, they break up really nicely when cold and hold their shape really well.