very horrifying

"very frightening"

trampled on

"walked on and crushed"

"the ten horns on the head of the fourth animal"

"grew up, and about the three horns that fell down in front of it" or "grew up, and about the three horns that fell down because of it"

Here "fell down" is a euphemism that means they were destroyed." AT: "which destroyed the three horns" (See: rc://en/ta/man/translate/figs-euphemism)

"its mouth that boasted" or "the mouth of the new horn, that boasted"

the horn with the eyes and a mouth seemed to be greater than the other horns