Starting with "Y":
* Yonder yellow yonder: This is a bit tongue-in-cheek, but it emphasizes the sound of "Y".
* Yappy young yorkie: This describes a small, energetic dog.
* Yawning yellow yeti: This creates a whimsical image of a tired, large, mythical creature.
Containing "Y":
* Playful purple parrots: This highlights the vibrant colors and playful nature of parrots.
* Shiny silver symphony: This evokes images of a beautiful and elegant performance.
* Dizzying, delightful daydreams: This describes fantastical and enjoyable thoughts.
Remember, alliteration is about the sound of the words, not necessarily the spelling. So, you can use "Y" at the beginning of a word or within a word to create an alliteration.