Rule 143.5

Units cannot be Attached to other permanents. See rule 435. Attach for more information on the attach game action. See rule 716. Attachment for more information on attachment.

• 143.5.a If a Unit would be Attached to a permanent, nothing happens.
• 143.5.b If a non-Unit Game Object that is Attached becomes a Unit through any means, it detaches as it becomes a Unit.

Official Core Rules