The pack is transparent light blue, with capitalized red writing that reads "Marsh King" and a crown on top of said writing.
Role in episode
SpongeBob and Patrick are pretending to be astronauts with some water helmets while eating the marshmallows. SpongeBob then offers some to Squidward, but the latter turns down the offer on grounds that he doesn't eat junk food. However, due to him being annoyed by their astronaut roleplay, Squidward then agrees to grabs one and tries to roast many marshmallows, keeps getting spit "molten foodstuffs" at him by Patrick. Later, when Squidward is playing his clarinet, SpongeBob shoots a marshmallow through his clarinet into his throat.
SpongeBob and Patrick believe them to be eaten by the astronauts.
Squidward considers this snack as junk food and indirectly says that Swedish Barnacle Balls are more appropriate to eat than Marsh King's marshmallows.
The name might be a parody of the fast food restaurant Burger King.