They are useful for changing terrain, with WaterPath and WaterTrail allowing them to make water tiles, while DrainWater can turn water into earth. Note that DrainWater also gives the Plant Mermaid magic charges and shields. They can also act as healers with SpawnHealFlower and Rejuvenate, though neither are a means of directly recovering Health.
Plant Mermaids can save you a lot on upkeep costs. As they have both Photosynthesis and Aquatic, they make excellent fishers at Home, acquiring food without eating any. Selling the rare fish they catch can also cover their salaries, essentially making them free to keep.
- Can magically create water to increase mobility of other water creatures. They also have access to strong skills.