As agreed, I'm sending you the sentences I rephrased myself.

Question

I'm looking forward to your prompt reply (as I need them for tomorrow). Thank you a lot

1) The breath of the dragon flared up from the rock and the ground boomed (re-echoed?)
Beowulf, concealed (“overshadowed”) by the mound raised his towering shield. Then he shook out (or drew?) his huge, ancestral, sharp-edged sword. The sword is described as an ancient relict (“heirloom”). Each felt terror at the other and wished the other dead.
2) The serpent slithered forward (“flowed forward”), coiled itself together and spat fire.
I still can paraphrase this line:
3) “The temper of the twisted tangle-thing was fired to close now in battle”. (does it mean that the serpent started to spit fire or that it lost its temper and spat out fire?).
4) Beowulf summoned the strength to swing his sword so hard that it snapped against the dragon's head. As it broke, it stroke the snake less strongly than required.
5) The snake became furious and started to spit death-fire.
5)Thristing for revenge ("seething with warspite"), the dragon charged a third time, seizing Beowulf by the neck with his poisonous fangs.
6) Beowulf is described as an intransigent but weakened (“sorely-straitened”) Lord of friends, a great chieftain and a brave warrior-King.
7) He embodies the courtly (?) ideal of the warrior: he is corageous, generous and strenuous. He is endowed with supernatural powers, too.
8) Actually, he can spend days under water, kill winged and fire-breathing monsters, which live underwater as well as underground.
9)The epic poem recollects historical events as well as (or together with?)supernatural and mythological tales

Answer 1

1. not "overshadowed" -- comma after "mound" -- "drew" not "shook out" -- relic (<~~watch the spelling) not "heirloom"

2. not "flowed forward" (snakes slither!) -- delete "itself together" -- "coiled up" is fine

3. for "temper" see verb definition 3 here: http://www.answers.com/topic/temper -- it means that the sword was made for close battle; it was a very well made sword.

4. use "struck" rather than "stroke"

5. "deadly fire" would be better than "death-fire" -- watch spelling ~~> Thirsting

6. "intransigent" is fine, but "weakened"???

7. watch spelling ~~> "courageous" -- I'd use "forceful" or "dynamic" rather than "strenuous"

8. Delete the comma after "water" and insert an "and" there -- without punctuation.

9. "as well as" is fine -- comma after "events"