Mem cake

Mem cakes are collectables in Octo Expansion.

Mem cakes are small items modeled after objects and characters from the world of Splatoon. They are said to be physical manifestations of Agent 8's lost memories, and are obtained as rewards for completing stages. They are categorized by the stations that dwell in the lines. The mem cakes and their descriptions are able to be viewed from the CQ-80.

Gameplay
Collecting all the mem cakes of a particular set will net players Gear from Iso Padre to use in multiplayer after clearing Octo Expansion. Collecting them all will get 30,000 C.Q. Points

Using the "Ask for Help" option if a test proves too difficult will reward player a mem cake, but it would be grayed out, the text would be in Marina's ink color, its name would be "Hazy Memory" with Marina's symbol right beside the name, and the poem would be replaced with "Your guess is as good as mine." It would remain this way unless the player clears the test for real. This does not, however, prevent the player from either getting gear from Iso Padre or unlocking playable Octolings.

Trivia

 * The mem cakes resemble erasers, specifically the kind that are shaped to look like certain things. This could be a reference to the fact that Agent 8's memories have been "erased" (whether or not they were deliberately erased is unknown).
 * The mem cakes also resemble kamaboko, a Japanese fish cake consisting of pureed fish that can be shaped into looking like various things. When mem cakes are viewed from a certain angle some white speckles can be seen reflecting off of it, where the same effect is also present on kamaboko.
 * All mem cake descriptions are written in poems, following the format; A, BB, A.
 * The poems also follow an 8-8-8 syllabic format.
 * In the Japanese version, the poems follow the 5-7-5-7-7 syllable format of tanka poems.
 * When viewing a mem cake it is possible to flick the mem cake by holding down the and tilting the  right stick towards a direction and then releasing it, causing the mem cake to spin in the opposite direction.
 * A Splatoon 2 Anniversary Famitsu interview with the developers reveals some info about the mem cakes:
 * The reason that test subjects such as Agent 8 get mem cakes from the facility is because it supposed to give the them proof that the "promised land" is real and that they existed in it before.
 * The mem cakes are Agent 8's thoughts; some of them are based on experience and memory while others are thoughts about how Agent 8 imagines Inkopolis looks like, inspired by the Inkopolis magazine seen in the metro. So the things that Agent 8 hasn't experienced yet, but still have a mem cake for, are inspired by the magazine.
 * Agent 8's mem cake for Marina are memories, but they don't personally know each other; Marina was known as a famous elite Octarian engineer.
 * When the developers were asked whether the mem cakes are are kamaboko or erasers, the developers said it was ok to think of them as erasers.
 * The Inkling Boy and Girl mem cakes that make up the line A set are designed after the, , and  amiibo respectively, having the same ink color and hairstyles (though with different outfits). The amiibo themselves are the characters on the packaging artwork of Splatoon and Splatoon 2.
 * The color of the Inkling Squid mem cake does not match any of the Inkling Squid amiibo, and instead matches Agent 8's own default ink color or the main color used in promotional material for Splatoon 2, being pink.
 * In the opening dialogue for the Squid vs. Octopus (Splatoon 2) Splatfest, there is a message about being that specific team will make you that specific species that comes down from the ancient Splatfest fax machine. When Marina wonders what it means, Pearl replies "Your guess is as good as mine.". This could be a reference to the writing when you have a "Hazy memory" mem cake.