Familiar

Familiars are magical creatures that act as companions for witches and spellcasters in The Sims 2: Apartment Life (when The Sims 2: Pets is also installed) and The Sims 4: Realm of Magic. Witches in The Sims 3: Supernatural get a moodlet that boosts spellcasting if they own a cat or a small pet, but these pets are completely normal otherwise.

The Sims 2: Apartment Life
If players also have Pets installed, witches can summon their own cat familiar called a spectral cat.

The Sims 4: Realm of Magic
In Realm of Magic, spellcasters can acquire magical familiars that can aid in spell casting. If players own Cats &amp; Dogs, they can make their pets familiars as well.

Trivia

 * Hey is a reference to Legend of Zelda's Navi who was a ball of light with wings and frequently yelled "Hey!"
 * Voidy is a reference to the Veild Voidcritter featured in The Sims 4: Kids Room Stuff.