Scriptures say that there are the personalities of Dharama, Earth and Yugas too. The chapter 1.17 of Śrīmad-Bhāgavatam (Bhāgavata Purāṇa) describe this in details:
Mahārāja Parīkṣit, who could fight one thousand enemies single-handedly, thus pacified the personality of religion (Dharma) and the earth. Then he took up his sharp sword to kill the personality of Kali, who is the cause of all irreligion.
When the personality of Kali understood that the King was willing to kill him, he at once abandoned the dress of a king and, under pressure of fear, completely surrendered to him, bowing his head.
Mahārāja Parīkṣit, who was qualified to accept surrender and worthy of being sung in history, did not kill the poor surrendered and fallen Kali, but smiled compassionately, for he was kind to the poor.
Sūta Gosvāmī said:
Mahārāja Parīkṣit, thus being petitioned by the personality of Kali,
gave him permission to reside in places where gambling, drinking,
prostitution and animal slaughter were performed.
So there should not be any doubt on these statements from Mahabharata:
Know that Duryodhana was Kali, and Sakuni was Dwapara. -Asramavasika Parva -> Putradarsana Parva of Mahabharata
Shakuni obtained absorption into Dwapara. -Svargarohanika Parva of Mahabharata