Swiftfoot Boots
Artifact — Equipment
Equipped creature has hexproof and haste.
Equip 
"Test 12: Boots now protect wearer from all hazards except blisters. Need to source better insoles." —Development log of Willa, Yotian artificer
Svetlin Velinov
Rulings
If a creature enters the battlefield under your control and gains haste, but then loses it before attacking, it won't be able to attack that turn. This means that you can't use one Swiftfoot Boots to allow two new creatures to attack in the same turn.
(wotc • 2018-03-16)
Rulings
If a creature enters the battlefield under your control and gains haste, but then loses it before attacking, it won't be able to attack that turn. This means that you can't use one Swiftfoot Boots to allow two new creatures to attack in the same turn.
(wotc • 2018-03-16)