Being primarily aquatic, mermaids are vulnerable to drying out on land. Extended exposure to sunlight can cause them to dehydrate and potentially harm their health.

As aquatic creatures, mermaids are not well-suited to environments with fire, and prolonged exposure can be detrimental.

Many myths portray mermaids as susceptible to magical influences, which can be used to control or harm them. 

Mermaids are often depicted with hearing similar to dolphins, making them vulnerable to the effects of intense or harmful sounds, including artificial sonar. 

Some myths portray mermaids as unable to survive indefinitely on land, requiring frequent immersion in water to stay healthy. 

While some myths may imbue mermaids with magical abilities, they are also often depicted as vulnerable to conventional weapons if struck in vulnerable areas, like the heart.