Friend (formerly known as No Name) is a blue jellyfish who only appears in the episode "Jellyfish Hunter." He is the smartest and stealthiest of all the jellyfish.
No Name is an average jellyfish with a blue body and seven navy blue/dark blue spots. He is the stealthiest and fastest of every known jellyfish SpongeBob had caught, not to mention being the smartest jellyfish of all due to his evasion maneuvers.
No Name was first seen in his debut and only episode where it avoided being caught by SpongeBob. After being sent by Mr. Krabs to catch every jellyfish for their jelly and the population of Jellyfish Fields was depleted, SpongeBob was followed by No Name when going back to his house where he was captured by the blue jellyfish when he cut the electrical wire and lured SpongeBob with a Krabby Patty made from his own jelly. No Name brought SpongeBob to a factory and showed him the inside where every jellyfish SpongeBob caught are being tortured and their jelly being extracted. SpongeBob then saw Mr. Krabs in the factory and was the one who tricked SpongeBob into catching the jellyfish just for money. The two of them stormed into the factory, stopped Mr. Krabs, and freed the remaining captured jellyfish who proceeded to sting Mr. Krabs. As thanks for rescuing his kindred, No Name allowed SpongeBob to catch him, and No Name was renamed Friend.
Like all jellyfish, No Name can create an electric shock/sting that makes the body parts of a hostile person to swell up. However, it is shown in "Jellyfish Hunter" that No Name can hold back his sting if, for any reason, he wishes not to harm someone (seen when No Name taps SpongeBob on the shoulder while inside the factory). No Name also has the ability of stealth, speed, and intelligence. It is shown also in "Jellyfish Hunter," that No Name is skilled at using a jellyfish net and a jar, therefore making him the smartest jellyfish.
BZZ, BZZ, BZZZZZ! [translated to "Bring it on!"]
[heavy breathing noises]
In the Morris Broadband description of the episode, No Name is called Ol' Buzzy.
There are other blue jellyfish shown throughout the series, mostly in older episodes, and in "The Pink Purloiner."