score:3
Greyhound has several night buses leaving Buffalo and arriving in New York City:
10:35 pm - 6:15 am
11:00 pm - 6:45 am
12:15 am - 7:30 am
3:10 am - 11:45 am
You can get to Buffalo from Niagara Falls by walking across the Rainbow Bridge ($1 CAD cash toll; bring a loonie) and catching the NFTA Route 40 bus ($2 USD cash fare) at Centennial Circle (1st and Rainbow) just a couple of blocks outside of customs. Buses leave there approximately hourly and take about 50 minutes to reach downtown Buffalo. But this bus route stops here in both directions, so take a bus signed Buffalo, not one signed Niagara Falls. They terminate at the Metropolitan Transportation Center which serves both local and Greyhound buses, so you don't have to go anywhere else.
Be sure to factor in 10-15 extra minutes for the border crossing as it gets busy in the afternoons/evenings even in the pedestrian lane.