Is Accelerate free on Rek'Sai Breacher?

No, Accelerate is not free when you have Rek'Sai, Breacher on the field.

According to RiftJudge FAQ #9725 and Rule 805.1.a, Accelerate is an optional additional cost. When Rek'Sai, Breacher grants the Accelerate keyword to a unit (such as a token played from an ability), it gives you the option to pay that cost to have the unit enter the board ready.

Here is how it works:

  • The Cost: The cost for Accelerate is [1] Energy and 1 Power.
  • Optional: You are not required to pay this cost. If you choose not to pay it, the unit will simply enter the battlefield exhausted (the default state).
  • Payment: If you want the unit to enter ready, you must pay the [1] Energy and 1 Power during the "Pay Costs" step of playing that unit.

In summary, Rek'Sai, Breacher allows you to use the Accelerate mechanic on units that wouldn't normally have it, but you must still pay the required cost if you want the benefit of the unit entering the board ready.