Killing Xanathar

Knowing that this may be your only opportunity to slay Xanathar you charge at it, blade in hand to finish it once and for all. You jump in the air and stab the beast in its main eye. It suddenly starts to move again, writhing in pain on the ground. It then stops moving and closes its eye. You look at once more just to check if it’s dead and tell yourself in an excited tone, “Seems dead to me!”