Although Gae Bolg warped the very reality it was thrown in; altering cause and effect itself to demand the slaying of it's enemy Gae Bolg had one weakness: Luck. Great luck could change a pre-determined fate. And it was with that knowledge that Gilgamesh reached into the Gate with two hands and extracted several items. 

In his left hand contained lucky charms, the divinely blessed items which gave their heroes great favour and blessing. It gave him the luck, the divine favour, to change the destiny that was "pre-determined" by Gae Bolg. As such, Gilgamesh was able to jump back and avoid the spear even as he took out the weapon in his right hand. 

The Original Nine Lives. The original Bow that would come to embody the feat of Hercules. 

Gilgamesh was about to counter Enkidu's Nine Lives with his own, knowing that the Shield of the Gods would not help him in this situation when Gaia appeared. Gilgamesh paid no attention to what the interloper said; one thing was for sure: 

He was interrupting their reunion. 

Infuriated, and seeing that Gaia was now right in between Gilgamesh and Enkidu, Gilgamesh did not hesitate in going through with his action and firing Nine Lives. Now, with Gaia in between them eighteen strikes, eighteen dragons, each capable of destroying a country and matching the power of the divine bull individually impacted Gaia, who had foolishly chosen to intervene in the battle.