Soul Scourge When Soul Scourge enters leaves battlefield same target?

[rice]

is it the same target for both when Soul Scourge enters battlefield and exits battlefield

[Arix]

The leaves-the-battlefield triggers says "that player", and it's referring to the player targeted by the first ability, so yes. Note that the leaves-play ability doesn't actually target anything.

[F16]

if the target player became an invalid target when soul scourge resolves would it be countered entirely?

[Arix]

No. The Soul Scourge spell itself doesn't target anything. It resolves, comes into play, and then its triggered ability targets the player. If the player were to become an illegal target, the ability would be countered, but Soul Scourge itself has already resolved.