Background :
When Dar Hilzernod is reinforcing, roll a black power die at the start of the overlord's turn. On a surge, every hero on the board suffers 1 wound (ignoring armor). This wound may not be prevented .
Reinforcing is the act of purchasing reinforcements during an encounter. Fortifying is what Lts do when they are within 1 trail of a dungeon.

Errata:
Change the word 'reinforcing' on Dar Hilzernod's card to 'fortifying'.

Where does the text in italics appear? It should be noted both in the background and in the question.

Galvancito1 said:

On the Dar Hilzernod card - as indicated by the errata changing the word on Dar Hilzernod's card.