Can you play Stupefy when there are no units on board just to pay 1 energy and draw 1 card?

Ruling: No, you cannot play Stupefy when there are no units on board. A valid target for the spell is required to play the card.

Nuances:

• The "do as much as you can" rule only applies during resolution, not when determining whether a card can be played
• Even though the card text has two separate sentences (targeting a unit and drawing a card), you still need a valid target to play the spell initially