"Buster's cousin (Arthur's Birthday)" is not an official name.
Buster's cousin (Arthur's Birthday)
Family Unnamed spouse
Buster Baxter (cousin)
Bitzi Baxter (aunt)?
Bo Baxter (uncle)?
Buster’s aunt (unknown family relationship)
Cartoon debut "Arthur's Birthday" (mentioned only)

Buster's cousin is an older cousin of Buster Baxter. Pickles the Clown provided entertainment at this cousin's wedding.

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