I am reading through the Road to Legend rules right now and I saw this phrase somewhere: "in additional to the usual one threat for every two surges he spends when making attacks."

I am not sure what this is referencing. I have only played as the overlord twice so far in regular descent non-campaign play and I thought surges rolled on the black action dice were worthless to the overlord. Can the overlord spend these surges when making attacks to generate additional threat?

Page 10 of the base game rules, under step 5 of the attack sequence...

Using Power Surges (Overlord): For every two surges the overlord player rolls during an attack, he gains one threat token. Any unused surges are lost.

This has been errata'd to only work on an attack that hits a hero (no attacking empty spaces to generate threat).

The Bash and Dark Prayer abilities from the Altar of Despair expansion also provide uses for surges, if a monster has them.

Yes, the overlord is always able to spend 2 surges to gain a threat, as long as the attack hits. Misses from range or X results don't give anything, and the attack has to target a hero. Also, the overlord can't save up spare surges; if he rolls only 1 surge each on two attacks, he doesn't gain a threat.

Thank you. I was unaware of that. I have played Descent a total of 3 times so far and Overlord twice. I am new to the game but loving it so far!