On a few of the delve perils it states to return X amount of enemies from the discard to the game box...why? What is the significance of this? I couldn't find anything about recycling the discard if you run out of a deck or anything, so i feel like I've missed something blatantly obvious here.

In the rules reference page 7, under Discarding:

If the enemy deck is expended, the party leader shuffles the enemy discard pile to form a new enemy deck.

Aha, thank you! I've noticed a lot of little missed lines like that. Like distributing damage to targeted enemies being another 1 liner in a side bar. Other than that I'm greatly enjoying this game.