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:
- Take up to two resources from your sideboard to your play deck
- 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.