If I want to put LeBlanc Leyend on chain, do I need to discard to put it on chain if I have no hand?

Yes, you must discard 1 card from your hand to put the ability of LeBlanc, Deceiver on the chain.

According to RiftJudge FAQ #10377, FAQ #10237, and FAQ #8686, the discard requirement in LeBlanc's ability is a cost. In Riftbound, a cost must be paid in full to activate an ability or place a triggered ability on the chain.

• If you have no cards in your hand: You cannot pay the required cost. Therefore, you cannot activate the ability or place it on the chain at all.
• The "Optional" Nature: While LeBlanc’s ability is a triggered ability that uses the word "you may" (making it optional), that choice only applies if you are able to pay the cost. Because you cannot pay the cost without a card in hand, you cannot choose to trigger the ability.

This is consistent with Rule 422.3, which states that when discarding is listed as a cost, the action must be able to be completed for the cost to be paid.