Council of Elrond

Can you play Longbottom Leaf and bring 0 resources from your sideboard?

Yes, because although the rules normally prohibit playing a short-event if doing so wouldn’t effect the board state (i.e. “just to discard it”; see Rule 5.1.2), resolving Longbottom Leaf involves 2 actions:

1. Take up to two resources from your sideboard to your play deck
2. Reshuffle

Since the text says “up to two” resources, and since you shuffle regardless of how many resources you take into the deck, you are legally allowed to choose 0 resources with Longbottom Leaf and then shuffle, meaning Longbottom Leaf did have an effect on the board state when it resolved, making this a legal play.