Sailor Mercury is one of the five original Inner Sailor Senshi of the Solar System, and was the third Sailor Senshi introduced in the manga. Her civilian identity is Ami Mizuno, or Amy depending the dub you follow. Her attacks and powers are based around water and ice, as well as intelligence and computers. This is the original depiction of the character created by Naoko Takeuchi.
She is voiced by Kate Higgins.
Legends of the Multi-Universe (Menslady's Story)
Sailor Mercury and the other Inner Scouts had been separated from Sailor Moon. Somehow they ended up in a very bad part of the Digital World: Nightmare Hills.
Fortunately, Commander Keen was able to find them via his Photachyon Transceiver. Then, they were found by Angewomon, Sailor Moon, Buzz Lightyear and Ghost Rider.
For the rest of the story, Sailor Mercury was an ally of the Angels.
The Protectors of the Multi-Universe
Sailor Mercury came with the other Inner Scouts to aid Olivia in her training to become Sailor Phobes.
Mercury Sabao Spray - unleashes a swarm of bubbles that cuts of an enemy's vision
Mercury Sabao Spray Freezing - an upgraded version of Mercury Sabao Spray that can freeze an enemy
Mercury Shine Aqua Illusion - summons a wave of icy water
Mercury Aqua Rhapsody - summons a harp of water on which Sailor Mercury plays a tune that summons waves of water
Mercury Aqua Mirage - summons a large pillar of water which unleashes very strong blasts of water energy
Mercury Eternal Power Make-up - allows Sailor Mercury to become Eternal Sailor Mercury
Mercury Shine Show Illusion - summons a wave of icy crystals