- Emma freezes Miriam once, almost killing her.
- The girls' Super-Power Meltdown whenever a full moon occurs.
- The mutation Emma goes through in a Season 2 episode after cutting her finger on a piece of coral. Her arm turns white and scaly and she starts to mutate into a monster.
- One episode has Cleo being depressed, and she swims out into the middle of a known shark breeding ground to die.
- The water tentacle that attacks the girls in Season 3.
Nightmare Fuel / H2O: Just Add Water