Wight of Precinct Six gets +1/+1 for each creature card in your opponents' graveyards.
Wight of Precinct Six’s ability applies only while it’s on the battlefield. In all other zones, it’s a 1/1 creature.
If Wight of Precinct Six is dealt lethal damage at the same time as a creature an opponent controls, they’re destroyed at the same time. It won’t get an additional +1/+1 from its ability in time to save it.