Do I have to pay the Deflect cost when picking Rengar from hand with Bone Skewer?

Ruling: No, you do not have to pay the Deflect cost. Cards in hand are not permanents, and Deflect is only active on permanents that are already on the battlefield. Additionally, the delayed stun trigger from Bone Skewer does not require paying Deflect because it does not target (the unit is programmatically selected).

Sequence:

• Bone Skewer resolves
• Opponent chooses a unit from their hand (no Deflect cost applies here since the card is not yet a permanent)
• The unit enters play
• The delayed stun trigger applies to the unit (no Deflect cost applies here since the effect does not target)

Nuances:

• Deflect only applies to permanents on the battlefield, not cards in hand
• Effects that programmatically select units (rather than targeting/choosing them) do not trigger Deflect
• If you were playing a spell that targeted a unit with Deflect already on the battlefield, you would need to pay the Deflect cost