Krsna, as His original form in Goloka Vrindavana, never leaves there to enter the material creation.

Krsna indirectly enters the material creation by expanding as His 4 armed Visnu form, who then plays the part of the original two-armed Kṛṣṇa in a facsimile of the original Vrindavana that is in the material creation.  

Krsna, the Supreme Personality of Godhead and cause of all causes, is the source of ALL Visnu and Narayana forms of God.

However, in Vrindavana no one really cares for that comment, they don't care if Krsna is God or isn't God, to them He is simply their best friend and well wisher who they all love unconditionally. Therefore, to all the gopas (boys) and gopis (girls), Krsna is simply the centre of their existence, who will do anything to always be with.

Also, Krsna is ALWAYS protecting His friends too, always looking after their welfare and looking out for them, never allowing anything or anyone to harm them. This is what the eternal Kingdom of God, Goloka Vrindavana, is really like that has baffled scholars, philosophers, religionists, and seekers of truth since time immemorial.

Who would ever think that child Krsna in Vrndavana is the original form of God, the cause of all causes, and NEVER leaves there as His original form. When Krsna does appear in the facsimile Vrndavana in the material creation, outside the Spiritual World of Goloka-Vrindavana, then that form of Krsna is His Visnu-tattva expansion only playing the part AS the original Krsna.

However, Krsna's older brother Balarama, also in the original Vrndavana in the Spiritual World, is already a Visnu-tattva expansion of Krsna, being Krsna's first expansion. 

So when that Balarama appears in the "facsimile Vrindavana" in the material creation, He expands Himself as the exact very same Lord Balarama, and appears in the material creation in Krsna's pastimes while simultaneously remaining in the original Vrindavana in the spiritual world with Krsna.

In Goloka Vrindavana in the Spiritual Sky, the sense of "time" is always experienced as the "eternal presence" because Krsna, Balarama, and Radharani NEVER leave there. This is inconceivable to most of us and comes under the heading of simultaneously one yet different teachings.

Srila Prabhupada - "Kṛṣṇa is the original Supreme Personality of Godhead, and Baladeva (Balarama) is Kṛṣṇa's immediate expansion. Both Lord Kṛṣṇa and Baladeva appeared as sons of Vasudeva, so both of Them may be called Vāsudeva. From another point of view, because Kṛṣṇa NEVER leaves Vṛndāvana, all the forms of Kṛṣṇa that appear elsewhere are His expansions." (BG As It Is Ch 10 Text 37)

Srila Prabhupada - "The original Lord Kṛṣṇa never leaves Goloka Vṛndāvana. All the plenary expansions are one and the same Viṣṇu-tattva, and there is no difference in Their potency." (SB Canto 3 Ch 1 Text 34)

Srila Prabhupada - "Ādi caturbhuja, the original expansions from Baladeva (Balarama), are Vāsudeva, Saṅkarṣaṇa, Pradyumna, and Aniruddha. All of Them are Viṣṇu-tattvas, or nondifferent Personalities of Godhead. In the incarnation of Śrī Rāma, all these different expansions appeared for particular pastimes. Lord Rāma is the original Vāsudeva, and His brothers were Saṅkarṣaṇa, Pradyumna, and Aniruddha.

Aniruddha is also the cause of Mahā-Viṣṇu, from whose breathing the Ṛg Veda appeared. All this is nicely explained in the Mārkaṇḍeya Purāṇa. In the incarnation of Lord Kṛṣṇa, Aniruddha appeared as the son of the Lord. The original Lord Kṛṣṇa NEVER leaves Goloka Vṛndāvana. All the plenary expansions are one and the same Viṣṇu-tattva, and there is no difference in Their potency." (BG As It Is Ch 10 Text 37)

Srila Prabhupada - "The biggest and highest planet in the brahmajyoti is Kṛṣṇaloka, or Goloka Vṛndāvana, where the Supreme Personality of Godhead, Śrī Kṛṣṇa Himself, resides. Lord Śrī Kṛṣṇa NEVER leaves Kṛṣṇaloka." (Sri Isopanisad 12)

Giriraj Swami - "The Visnu who appeared in Mathura is Vasudeva Krsna, fully grown, with four hands and long hair and many ornaments and symbols of Visnu. The Krsna who took birth in Vraja is the original Krsna with two hands. When Vasudeva and Devaki prayed to Visnu as the Supreme Personality of Godhead to become like a human baby and Vasudeva carried him across the Yamuna River to Vrindavana, the original Krsna absorbed the Vasudeva Krsna into Himself." (Lecture Mumbai 1980)

When Krsna wants to fight demons, He does that as His Visnu-tattva expansion playing the part of Krsna in the material creation. In the original Vrndavana, there are no demons.

It is only the 4 armed Lord Visnu, playing the part as the 2 armed formed Krsna who kills demons in the facsimile of Vrindavana in the material creation. So, there are NO demons in Vrindavana in the Spiritual World of both Vaikuntha and Goloka-Vrindavana, so Krsna NEVER fights demons there.

Vaikuntha means without anxiety, so how can there be demons there? Prabhupada has said. Demons only exist in the "facsimile Vrindavana" in the material creation.

Krsna in "His original form" appears "via His Visnu-tattva expansion" to "one" Dvarpara-yuga out of every thousand, which is once every 8 billion 640 million human years.

But ONLY as His Visnu-tattva expansion of His original self playing the part AS Krsna. This is because Krsna, as His original form, as already explained, NEVER leaves Goloka Vrindavana in the spiritual world.*^