The US retail video game industry suffered yet another depressing month. Despite solid showings from titles like The Witcher 3: The Wild Hunt, Mortal Kombat X and Grand Theft Auto V, overall sales last month slid 13 percent year-over-year to $507.6 million according to a new report from industry analytics firm The NPD Group.

On an individual basis, software sales generated $204.7 million, down 25 percent from the $273.9 million generated in May 2014. Sales of hardware, meanwhile, dropped 18 percent to $153.6 million. Gaming accessories like Nintendo's amiibos were the saving grace for the industry, bringing in $149.3 million. That's up 20 percent compared to the year-ago period.

NPD analyst Liam Callahan said the decline in May 2015 is attributed to poor comparisons to a strong release slate in May 2014, specifically the launches of Mario Kart 8 and Watch Dogs.

In the heated next-gen console war, it was Sony's PlayStation 4 that came out victorious over Microsoft's Xbox One for the month of May.

As always, it's worth pointing out that NPD only tracks new physical games sold at retailers in the US meaning it excludes used games, digital downloads, mobile games and titles of any kind sold outside of the states. That said, the report is still quite insightful as it gives a pretty good snapshot of a particular market in the US.