19 down: Ubiquitous John a young herbivore (3)
18 across: Tail-ender (Indian mid-off) caught by famous 19-down (doe) misled into ferocious drive (5, 8)
These go a young herbivore = doe = Doe = ubiquitous John and tail-ender (Indian mid-off) caught by famous doe misled into = l Indian – ian caught by Bambi tion = blind ambition = ferocious drive.
There’s one relatively minor issue: a doe is a female herbivore, not necessarily a young one.
But as Caitlin pointed out, the actual error comes from famous doe = Bambi. Unbeknownst to a lot of us, including DA it seems, Bambi was male! Hence, he was never a doe, although once upon a time he was young.