In The Merlin Conspiracy, the enchanter Romanov is a wizard with a way with animals. He lives on an island which he's constructed of bits of multiple worlds, including a slice of land and a section of ocean to go with it from each source world. It is also set off in time ten years from most of the parallel worlds that are looked after by Magids. Romanov, however, is adept at making his way through the dark paths between worlds, and he has built a beautiful modern house with an elaborate attached garden, in which he raises chickens and one rather mad goat named Helga.
Protagonist Nick Mallory (Nichothodes Koryfoides) comes to Romanov's island while Romanov is down with a life-threatening magical illness, but he's able to pry from Romanov on his sickbed the secret to obtaining goat food. Regardless, the goat shows her obstinacy by taking a good share of everybody else's food, not to mention some of Romanov's furniture. She is clearly a handful.
Unusually, Helga takes a place as a character in the book, as she takes a fancy to Magid Maxwell Hyde who has visited the island and treated her in a masterful way. The obsession she develops causes her to follow after Hyde, and she shows up in the enchanter's London back garden in his home on Blest. Which is a lucky thing, since Hyde is rendered helpless by enemies, and the protagoists are only able to escape and find allies by grabbing hold of and following the goat to their destination. Once they arrive, she promptly has twin kids, and that is the last we hear from her. But she's mad, bad, and hard to forget.