Buy RS3 1/3 green blubber jellyfish
The 1/3 green blubber jellyfish is the last bite of a green blubber jellyfish in RuneScape 3. A full jellyfish is eaten in 3 bites. After two bites, this 1/3 piece is left. Eating it heals up to 500 life points and does not lower your adrenaline. That makes it a handy food for combat, since you keep your adrenaline while you heal.
The healing can be boosted. Expensive spices add 50 life points per bite. A necklace of gluttony adds 100 life points per bite.
You can also turn 1/3 pieces back into whole jellyfish. Take them to the clan representative at War's Retreat, Granny Rowan at Fort Forinthry, or Jellyfish Mender Judd at the Deep Sea Fishing Hub. Combining the pieces yourself in your bag does not work.
Green blubber jellyfish are members-only items. They are tradeable and noteable, but they do not stack. The 1/3 piece is a cheap way to top up your health, and it works well as extra food on long fights or bossing trips.