Smudging and blending colors can be a challenge,especially with the wrong tool.After trying numerous pencil brushes didn't do the trick for me,because the result was never precisely smudged.I had shadow all over my under eye area X_X.After analyzing the problem I came to a conclusion: The tip of the pencil brush is not stable enough to withstand the blending motion,so it kind of goes everywhere.
Soo I had an idea a while ago for a brush that blends like an eyeshadow brush ,but has enough stability to withstand vigorous blending motions.
eyeshadow brush that you won't miss(The ones included in eyeshadow palettes are great for that job)
Trim off any stray bristles and unwrap.
There you go,a perfect brush :)
If your eyeshadow brush is very soft,you may wanna cut it a bit shorter.
Here you can see how beautiful it smudges lines.