Dragon Slayer 4(Legacy of the Wizard) Kraugen

ドラゴンスレイヤー4 ドラスレファミリー キャラクター図鑑

Kraugen / クラウゲン

Official illust
Manual / Kadokawa guidebook

JICC guidebook

Basic info

Kadokawa guidebook
It is a giant freshwater poisonous jellyfish from South America and the middle Amazon River, colorless and transparent. Its skin is so faintly luminous that its outline is barely visible. It can swim freely in the air as well as in the water.
JICC guidebook
It hops around on the ground with its translucent body. It's a bit tricky when it comes down from above.

In the NES ver. of the manual, the name of this is "Invisigel".