When Lord Sri Krsna descends into the material world, all His plenary portions also appear with Him to exhibit different functions of the Lord. But for the pastimes at Vrndavana, all functions are performed by the Lord's different plenary expansions

Expressions researched:
"When Lord Śrī Kṛṣṇa descends into the material world, all His plenary portions also appear with Him to exhibit different functions of the Lord. But for the pastimes at Vṛndāvana, all functions are performed by the Lord's different plenary expansions"

Srimad-Bhagavatam

SB Canto 3

Lord Śiva, one of the three qualitative incarnations of the Personality of Godhead, is the plenary expansion of the Lord. Kārttikeya, born of him, is on the level of Pradyumna, another son of Lord Kṛṣṇa. When Lord Śrī Kṛṣṇa descends into the material world, all His plenary portions also appear with Him to exhibit different functions of the Lord. But for the pastimes at Vṛndāvana, all functions are performed by the Lord's different plenary expansions.

SB 3.1.30, Translation and Purport

O gentle one, does Sāmba fare well? He exactly resembles the son of the Personality of Godhead. In a previous birth he was born as Kārttikeya in the womb of the wife of Lord Śiva, and now he has been born in the womb of Jāmbavatī, the most enriched wife of Kṛṣṇa.

Lord Śiva, one of the three qualitative incarnations of the Personality of Godhead, is the plenary expansion of the Lord. Kārttikeya, born of him, is on the level of Pradyumna, another son of Lord Kṛṣṇa. When Lord Śrī Kṛṣṇa descends into the material world, all His plenary portions also appear with Him to exhibit different functions of the Lord. But for the pastimes at Vṛndāvana, all functions are performed by the Lord's different plenary expansions. Vāsudeva is a plenary expansion of Nārāyaṇa. When the Lord appeared as Vāsudeva before Devakī and Vasudeva, He appeared in His capacity as Nārāyaṇa. Similarly, all the demigods of the heavenly kingdom appeared as associates of the Lord in the forms of Pradyumna, Sāmba, Uddhava, etc. It is learned here that Kāmadeva appeared as Pradyumna, Kārttikeya as Sāmba, and one of the Vasus as Uddhava. All of them served in their different capacities in order to enrich the pastimes of Kṛṣṇa.