As a reaction, which you use when you or another creature that you can touch or see within 10 meters makes an attack roll, an ability check, or a saving throw, the creature has a second chance. The creature makes the roll with advantage or with disadvantage (your choice). You can do so after the roll but before any effects of the roll occur.
If the roll already has advantage or disadvantage, you cannot apply another instance of advantage or disadvantage and you must use this before the roll to cancel out any advantage or disadvantage.
You can provide a second chance for one additional creature for each additional mana expended. The creatures must be within 5 meters of each other when you target them.