Leuko

A Leuko is a large jellyfish-like enemy found in The Sea and the Sunken Ship in Super Mario RPG: Legend of the Seven Stars. It is an enemy with fairly high HP, is immune to Thunder-Based attacks and knows only 3 attacks - Bolt, Static E!, and Solidify.

Trivia

 * Leukos may be related to Muckles or Jelectros.