That is BN 4
Dark Chip only appears when the emotion is anxious
No, in BN 4, We can't freely choose a Dark chip that we wanted
There are only 2 dark chips that can be selected in Custom Window
Only appears when Rockman is anxious
The Dark chips change every turn as long as Rockman is still anxious
While in BN 5, you can use Dark chips as one of the chips in your folder
You can load up to 3 Dark Chips in your folder
Thus, it can appear anytime, when you open the Custom Window
I don't know about this, but
In BN 5, when you are using Dark Rockman,
The probability of Dark chip to be appeared in your Custom Window, is increased