The goblins, after trying many times (гоблины, попробовав много раз: «после попробовав много раз»;
The goblins, after trying many times, managed to creep over the rocks behind the dragon, and throwing the dust which the rabbit had given them into its flaming eyes they at last, after a hard fight, killed the monster and entered the cave.
The goblins looked round in the darkness for the serpent (гоблины осмотрелись вокруг в темноте в поисках змеи) of which they had heard (о которой они слышали;
At last, when they were sadly thinking (наконец, когда они /уже/ печально собирались: «думали») of going back to the boat (вернуться к лодке;
It was the serpent's tail (это был хвост змеи)!
The goblins looked round in the darkness for the serpent of which they had heard, but they could not find it.
At last, when they were sadly thinking of going back to the boat, Red-Cap cried out that he saw something yellow in the dark shadow of a rock.
It was the serpent's tail!
They all ran after it (они все побежали за ней), shouting loudly (громко крича;
It went very quickly (она продвигалась очень быстро;
They all ran after it, shouting loudly, and it led them some way down a rocky passage.
It went very quickly, and they had to run very fast to keep it in sight; but at last they caught it, and after a sharp struggle—in which poor little Red-Cap nearly lost his life—killed it.
The three little brothers stood looking at the dead serpent (три братца стояли, глядя на мертвую змею), and while they were looking (и пока они смотрели на нее) it seemed to change (стало казаться, что она меняется: «она казалась меняться»)! It moved (она двигалась)! and grew thinner and darker (и становилась тоньше и темнее), and the bright yellow colour turned to orange (и яркий желтый цвет превратился в оранжевый), and from orange colour to red (а из оранжевого цвета — в красный), and then redder (и затем краснее = стал еще краснее)! and redder!! and redder!!! until they saw (пока они не увидели: «пока они увидели»)—that it was no longer the serpent (что это не была больше змея;