2020-09-25 : Attaching an Equipment with its enters-the-battlefield triggered ability isn’t the same as using its equip ability. You don’t pay mana for the attachment, and if the Equipment enters at a time you couldn’t cast a sorcery, you can still attach it to a creature you control.

2020-09-25 : If the target creature becomes an illegal target, the Equipment remains on the battlefield unattached.