Focusing on their appearance:
* Glimmering gelatinous globes
* Jello-like, jiggling jellies
* Shimmering, silken sea stingers
* Transparent, translucent tentacles
Focusing on their behavior:
* Floating, fragile, fantastic fauna
* Mesmerizing, mysterious marine marvels
* Swaying, silent, serpentine swimmers
* Whirling, whispering, wonderous wonders
Focusing on their impact:
* Painful, poisonous, prickly predators
* Stinging, shocking, slippery sea creatures
* Troubling, treacherous, tentacled threats
You can also use alliteration to describe specific types of jellyfish, like:
* Boxy, brilliant, blue box jellyfish
* Magnificent, majestic moon jellyfish
* Pink, pulsing, Portuguese man-of-war
Remember, alliteration is all about creating a fun and memorable sound, so feel free to play around with different words and phrases!