If you remember what I said about Toa Mercurex's former team ? If you did , she is the toa that killed the other members of the team. She, was one of Mercurex's most powerful members( yes, Mercurex was the leader ). Until they all left her when they were attacked by a group of Vahki , thinking that she can handle it , she almost died . Feeling unwanted , she killed everyone of her former teammates , leaving Mercurex , but luckily he survived heading to Arka nui . She followed him , until she met Makuta Toxic . Then she joined the Battalion of Darkness giving her a new name " Desire" ( and her real name is still unknown for the mean time).
"Come and get me" - Desire to Mercurex
Like Makuta Toxic's staff except you became a liquid state and can only be cured IF every single drop is there , and if a toa of water forms the shape of the victim, and will soon became his/hes solid / normal state.