Hydromander is a one-shot minor antagonist of the reboot TV series, Ben 10. It first appeared in the episode, Water Filter.
Ben transformed into Cannonbolt and did a cannonball dive in Niagara Falls. What he just did disturbed the sea monster, Hydromander. The next day, it attacked. Ben transformed into Overflow and fights it and it got defeated. After it got defeated, its body started to form many smaller Hydromanders. Overflow did a cannonball dive and all small Hydromanders were splashed into land and died.
The Hydromander is a gigantic green monster, which is most likely an amphibian. It resembles an axolotl.
The Hydromander is a dimwitted monster, who only wanted destruction.