Barbarian suggests:
Let's test that belief. Give us any two major groups of organisms, said to be evolutionarily connected, that lack transitionals.
Show us what you have.
Australopithecines fit nicely between humans and other apes. Would you like to see the list of transitional features in Australopithecines?
Who's "slim?" Did you mean the creationist misconception that humans evolved from slime?
Actually, fish evolved into tetrapods, land vertebrates, not humans. That was later. But Acanthostega is a great transitional form between fish and tetrapods. Want to learn about the transitional features of Acanthostega?
While the existence of all these transitional forms is compelling evidence for evolution, what's even more compelling is that there are no transitional forms where they shouldn't be. No feathered mammals, no arthropods with bones, no whales with gills.
That's a much more devastating blow against YE creationism.