The Pinyin final "Ø1" is used in the second half of Pinyin syllables. In MandarinBanana's mnemonic system, the second half of a Pinyin syllable is always represented by a location. You can visit the Pinyin index to see all Pinyin syllables from this mnemonic group, or to see all Pinyin syllables "Ø1" can appear in.
“Ø” as the second half of a pinyin syllable means in the Marilyn Method system that there simply is no second half. Pronounce the start of the syllable on its own without dedicated ending.
The only exemption is “er”, which is arbitrarily assigned to the initial syllable “Ø” and ending syllable “Ø”.