There is a leela about Krishna-Kali Roopa of Sri Shyamsundar. I do not remember the source, but this leela is well-known in Vrindavan too, and is recounted in the legend of Krishna-Kali Temple of Vrindavan.
Once Srimati Radharani was enjoying the mellows of Divine Love with Sri Keshava, when Kutila, the sister-in-law of Sri Radhika, complained to Ayan Ghosh that his wife was saluting with Sri Krishna.
When Ayan went to check the truth for himself, Sri Krishna told Srimati Radha to quickly gather some flowers and assume a worshipping posture, while Sri Krishna transformed into the form Sri Krishna Kali.
So, when Ayan reached the spot, he found Sri Radha devotedly worshipping Jagadambika Kalika, the Ishta Devi of Ayan himself. The latter was pleased at the sight and left.
This is the Divine Leela of Sri Krishna assuming the form of Krishna-Kali, which is celebrated on the day of Dipavali at Sri Radha Shyamsundar Mandir in Sripat Khardah.