Rulings

If multiple creatures enter at the same time, Flame-Kin War Scout's ability will trigger multiple times. When the first of these triggers resolves, if Flame Kin War Scout can be sacrificed by the ability's controller, it will be sacrificed and deal 4 damage. When the other triggers resolve, it won't be on the battlefield, so it can't be sacrificed and the other creatures won't be dealt any damage.