What about the giant cat?
In the beginning of the movie the creatures enlarged by "The Goo" are in order:
A stray cat (which threatens the main characters Tommy Kirk as Mike, Nancy Charla Doherty as Nancy, Ronny Howard as The Genius) which is then chased off by the barking dog. The enlarged stray cat is never seen again in the film.
Two ducks are enlarged by The Goo. One is verifiability later killed then eaten at a barbeque (shown roasted on a spit over an open flame). The whereabouts of the other giant duck is unknown.
The family dog is enlarged by The Goo. It is later returned back to normal size near the end of the movie and remains alive to the movie end.
A brown hairy tarantula spider (improbable to find unless it was a pet of The Genius) is enlarged by The Goo in the basement lab of The Genius. It is killed by electrocution when Mike kicks loose a water pipe and electrocutes the spider with a dose of household electricity from a broken lightbulb on a line.
Shortly thereafter, a few members of the gang of weird party-obsessed teenagers break into the basement lab of The Genius and steal The Goo. They divide up The Goo and enlarge themselves into giants (per the title of the movie). All of the giant teenagers are returned to normal size and remain alive by The Genius and his yellow colored smoke bomb antidote.
Note that after the teenagers turn themselves into giants and hold the town hostage, The Genius creates an orange-red hydra creature which then crawls out of the Conical Flask down the drain of his lab sink to never be seen again except in the 1975 movie, "Shivers" by David Cronenberg (also known as "They Came From Within").
No other animals or humans are enlarged in the movie.
Creatures not killed or normalized at the end of the movie are the enlarged giant cat and the condition unknown giant duck.