|Breath of Fire II Boss|
おおみみず Oo Mimizu (Great Earthworm)
Ryu should use a Dragon transformation, and then constantly attack. Sten should use Spark (or Flame if he knows it) and Nina should use S.Boom. Rand should attack and heal when needed. It's a good idea to have Nina and Sten in the rear of the defense formation, because they have low HP and Defense and their spell damage doesn't take a penalty.
J.Worm frequently uses SwtBrth, which can put party members to sleep. They can be woken with Rand's Wake skill or Nina's regular attack, but unless most party members are sleeping the party should focus on dealing damage.