When Rek'Sai gives units played from other places Accelerate, do you have to pay the 1 energy and 1 power cost, or do they accelerate for free?

Ruling: You must pay 1 energy and 1 power (of the unit's domain color) as an additional cost to have the unit enter ready.

Nuances:

• The Accelerate keyword is shorthand for "You may pay 1 energy and 1 power as an additional cost to have me enter ready"
• The power cost is always the color of the unit's domain (or universal if it has no domain)
• Reminder text in parentheses is not rules text; keywords represent specific rules-literal phrasings