Within this fist sized vial is a bright aquamarine water, clear as crystal, that refracts light that passes through it. When poured out onto the ground it reaches from the ground to form tentacles that whip into a Large four legged creature. This creature has the body of a horse but at the end of its graceful neck is the head of a sea creature. It is the same color as the water within the vial but is now mostly opaque, and has a dark mane. It is equipped with a saddle, bit, and bridle, especially made for its physique and all out of white leather. Any of this equipment dissolves into a puddle of water if carried more than 10 feet from the steed.
The steed will remain for the next 10 hours and slowly dissolve into a puddle over the course of 1 minute allowing the rider to dismount. However it will abruptly convulse into a mist if it takes any fire damage, is reduced to 0 hitpoints, enters into an environment of extreme cold, or extreme heat.
The steed uses the statistics for a warhorse, except it has a speed of 80 feet, and a swimming speed of 40 feet. You can ride it as any other well trained mount and it will do its best to avoid taking damage until you give it a command. When the steed is destroyed or reaches the end of its time it returns to the vial if it is open and will not form again for 1d4 days. If the vial is not open it will wait until the next dawn to attempt to return to the bottle before leaving for the plane of water.