It's called Rift Of The NecroDancer, and it's a "standalone rhythm game in the NecroDancer universe." You can watch its surprise reveal below, at the end of the trailer for the newly released Synchrony DLC for Crypt Of The NecroDancer.

A rhythm game but not a roguelike?

While a new standalone game is instantly exciting, the Synchrony DLC released in Steam Early Access today is no slouch?

It's the first expansion for Crypt Of The NecroDancer since the Amplified DLC launched in 2017.