You can now enter a custom seed when picking a difficulty mode or leave it empty to just use a randomly generated seed.
You can also view seeds by going to the pause menu to record or share the seed for others to try too.
The seed will also show on death or escape.
For those who don't know seeds let the randomness of the game be re-generated exactly as according to the seed value.
The only thing that is not re-generated with the same seed value are what non-puzzle notes get spawned and where.
Regards,
George