Mystery snails naturally produce and leave slime on any surface they touch. This slime is produced by a special gland on the front part of their muscular foot, and is believed to help them move more efficiently.
However, mystery snails still excrete this slime even when they’re not moving, so don’t be surprised to see slime trails on your tank’s walls or substrate.
That said, excessive slime production is not normal in mystery snails. If your mystery snails are suddenly excreting more slime than usual or discolored slime, they might be stressed or unwell. Immediately check the water parameters and keep them away from any possible stressors.