What are the side effects of laser hair removal that can look badly?

Typically, none. Usually there are no long-term changes to the skin, other than less hair. Because there is some uncertainty in selecting the optimal dose of laser energy for each individual, there is a small chance (1% or less) of burns or pigment changes in the skin. These usually heal and improve with time, but they can rarely result in scarring or permanent pigment changes.
Pigment change, scar. Laser hair removal is generally a safe and effective procedure. However complications can occur. These include a change in the pigmentation of the skin, either lighter or darker, and scarring. Darkening of the skin is usually temporary. Patients with a tan and darker skin types are at more risk. See an experienced dermatologist or aesthetic physician in order to minimize risk of complications.