Mucus in the baby's stool is usually a thick fluid like secretion. It is common in babies that are breast fed.
I hope this was helpful.
Mucus in the stool is normal if there's a small amount of it. Large amounts could mean a sign of an allergic reaction. If breast-feeding, try to avoid dairy products from your diet as well as no nuts and shellfish. If you use formula try switching to soy. If that doesn't work you'll have to use hypoallergenic formula.
I recommend addressing your concerns with your pediatrician and asking them about what foods to avoid or which formula to use.