Groom's Finery
Artifact — Equipment
Equipped creature gets +2/+0. It gets an additional +0/+2 and has deathtouch as long as an Equipment named Bride's Gown is attached to a creature you control.
Equip 
(: Attach to target creature you control. Equip only as a sorcery.)
Eric Deschamps
Innistrad: Crimson Vow (VOW)
• #117Rulings
In the phrase “as long as an Equipment named . . . is attached to a creature you control,” the “you” is the controller of the Equipment, not the controller of the creature it's attached to. Suppose an opponent controls a creature equipped with Bride's Gown and another creature equipped with Groom's Finery, and they also control both of those Equipment. If you gain control of one of those creatures but not the Equipment attached to it, the creature you gained control of will get all the bonuses and the creature they control will only get +2/+0.
(wotc • 2021-11-19)
Rulings
In the phrase “as long as an Equipment named . . . is attached to a creature you control,” the “you” is the controller of the Equipment, not the controller of the creature it's attached to. Suppose an opponent controls a creature equipped with Bride's Gown and another creature equipped with Groom's Finery, and they also control both of those Equipment. If you gain control of one of those creatures but not the Equipment attached to it, the creature you gained control of will get all the bonuses and the creature they control will only get +2/+0.
(wotc • 2021-11-19)