Swiftfoot Boots

Artifact — Equipment

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and no matter when it came under your control.)

Equip ( : Attach to target creature you control. Equip only as a sorcery.)

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.