Does Rell have to pay power costs for equipment in hand when using ability?

To determine if you must pay the Power cost for an Equipment played via Rell, Magnetic's ability, we must look at the specific wording of her ability and the rules regarding "ignoring costs."

Ruling

No, you do not have to pay the Power cost.

When you use Rell, Magnetic's ability to play an Equipment, you are instructed to "play an Equipment... ignoring its cost." According to Rule 353.1.a, when a card allows you to play a card "ignoring its cost," both its base Energy cost and base Power cost are set to zero.

How it Works

1. Trigger: Rell's "When I attack" ability triggers.
2. Choice: You choose an Equipment in your hand with an Energy cost of 2 or less.
3. Cost Setting: Because the ability instructs you to "ignore its cost," the base Energy and Power costs of that Equipment are set to 0 (Rule 353.1.a).
4. Playing the Card: You play the Equipment. Since the costs are now 0, there is no Energy or Power cost to pay.
5. Attachment: The ability then instructs you to attach it to Rell. You do not pay the Equip cost for this initial attachment because it is happening as part of the card's effect.

Summary:

• Base Costs (Energy/Power): Set to 0 by the "ignoring its cost" instruction.
• Equip Cost: Not paid, as the attachment is part of the ability's effect.

Note: I could not fully verify this ruling against the retrieved rules.