Strider Harness
Artifact — Equipment
Equipped creature gets +1/+1 and has haste.
Equip 
(: Attach to target creature you control. Equip only as a sorcery.)
"Because the giant, implacable death lizard wasn't scary enough already." —Captain Brinely Rage
Kev Walker
Rivals of Ixalan (RIX)
• #183Rulings
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 Strider Harness to allow two new creatures to attack in the same turn.
(wotc • 2018-01-19)
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 Strider Harness to allow two new creatures to attack in the same turn.
(wotc • 2018-01-19)