Mermaids cannot choose when they change, and change upon contact with water.

Mermaids feel very strongly drawn to the water.

Mermaids have extremely strong intuition, and with enough training can harness this power to predict what will happen next.

The mermaid gene is genetic. A mermaid is activated when they fall in love for the first time. This is when they unlock the gene.

Mermaids can always sense other mermaids.

Sirens can choose when they change. Sirens have tails similar to mermaids.

Sirens can make anyone do and feel anything, simply by softly singing/humming/speaking with their siren musicality.

The siren gene is not genetic, it can strike anyone at birth.

Sirens are more common than mermaids.

Sirens can always sense other sirens.

When a siren sirens someone, only the siren who sirened can undo that siren. Say it five times fast.

Sirens cannot siren their own blood.