Bramble Armor
Artifact — Equipment
When this Equipment enters, attach it to target creature you control.
Equipped creature gets +2/+1.
Equip 
(: Attach to target creature you control. Equip only as a sorcery.)
Alessandra Pisano
Rulings
Bramble Armor doesn't enter the battlefield attached to a creature. Instead, the Equipment enters the battlefield and then a triggered ability attaches it to a creature. You may cast Bramble Armor even if you don't control any creatures.
(wotc • 2021-11-19)
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 the timing restrictions for equip abilities don't apply.
(wotc • 2021-09-24)
If the target creature becomes an illegal target, the Equipment remains on the battlefield unattached.
(wotc • 2021-09-24)
Rulings
Bramble Armor doesn't enter the battlefield attached to a creature. Instead, the Equipment enters the battlefield and then a triggered ability attaches it to a creature. You may cast Bramble Armor even if you don't control any creatures.
(wotc • 2021-11-19)
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 the timing restrictions for equip abilities don't apply.
(wotc • 2021-09-24)
If the target creature becomes an illegal target, the Equipment remains on the battlefield unattached.
(wotc • 2021-09-24)