Kṛṣṇa has all of His 64 qualities in full all the time unlike all the other variety of living entities who only partially exhibits such attributes.

Krsna is likened to the original candle that lights all other candles of the same luminosity.

Furthermore, Krsna as His original Form has 64 qualities of which 4 of those are unique to only Kṛṣṇa only partially exhibited by some other expansion.

Krsna as His original childhood form never leaves Vṛndāvana.

Srila Prabhupada - "Kṛṣṇa as His original childhood form NEVER leaves Vṛndāvana, all the forms of Kṛṣṇa that appear elsewhere are His Viṣṇu-tattva 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 - "Kṛṣṇa is the original Supreme Personality of Godhead, and Baladeva (Balarama) is Kṛṣṇa's immediate expansion. Because Kṛṣṇa NEVER leaves Vṛndāvana, all the forms of Kṛṣṇa that appear elsewhere are His expansions." (BG, As It Is Ch 10 Text 37)

Kṛṣṇa’s first expansion is Balarama, and from Balarama ALL Visnu-tattva expansions originate.

When the "original" Krsna wants to enter the material creation to perform His pastimes in the Vrindavana facsimile of the spiritual world, His Visnu-tattva expansion, coming from Balarāma, performs those Kṛṣṇa pastimes or lilas.

In other words, because the original Kṛṣṇa NEVER leaves Vṛndāvana, His Visnu-tattva expansion coming from Balarāma, plays the part of the original Kṛṣṇa in the material creation that includes killing demons there.

When Kṛṣṇa wants to enter the Vaikuntha planets, and the material creation, He first expands Himself as Balarāma (His older brother in Vṛndāvana) and from Balarama, all Visnu-tattva expansions manifest.

This includes a Visnu-tattva expansion of Balarāma who plays the part of the two-armed Krsna who enters the material creation and even kills many demons.

Such killing of demons do not happen in the original Vṛndāvana in the Spiritual worlds, it only happens in the "facsimile of the original Vṛndāvana" that is in the material creation that is almost non-different than the original.

No Visnu-tattva expansion has those 4 extra qualities Krsna has all the time like Krsna does, they can have them partially only. 

Therefore Krsna is always the Supreme Personality of Godhead and cause of all causes and can expand into innumerable categories of living entities. 

Of those living entities, the ones who are almost equal to Krsna are called Visnu-tattva.

Others living entities like jiva-tattva (jiva-souls) are more independent from Krsna who each have their own unique personality separate from Krsna's Personality. 

Srila Prabhupada - "The "immediate" expansions of the Lord are called svāṁśa or personal direct expansions (Visnu-tattva who are Krsna playing another role in His own pastimes) The "separated" expansions of the Lord are called vibhinnāṁśa - (jiva-tattva) or independent jiva-souls like us." (From BG, Ch 10 Text 37, Purport)

Another living entity, Siva-tattva, is neither Visnu-tattva or jiva-tattva but is in a league of his own. All are Krsna's expansions each having a portion of Krsna's 64 qualities. However, only Kṛṣṇa has all 64 qualities in full all the time.

Visnu-tattva expansions have 60 of Krsna's 64 qualities which is 93.75% of Krsna's 100% attributes. 

Siva-tattva expansion has 55 of Krsna's 64 qualities which is 85.938% of Krsna's 100% attributes.

Jiva-tattva (jiva-soul) expansion has 50 of Krsna's 64 qualities which is 78.125% of Krsna's 100% attributes.

Being all-powerful Krsna can expand Himself into forms with the same power and characteristics He possesses, without diminishing Himself in anyway.

Srimad Bhagavatam - "All of the incarnations are either plenary portions or portions of the plenary portions of the Lord, but Lord Śrī Kṛṣṇa is the original Personality of Godhead. All of them appear on planets whenever there is a disturbance created by the atheists. The Lord incarnates to protect the theists." (SB, Canto I Ch 3 text 28)

Srila Prabhupada - "Learned scholars in transcendental subjects have carefully analyzed the summum bonum Kṛṣṇa to have sixty-four principal attributes. All the expansions or categories of the Lord possess only some percentages of these attributes. But Śrī Kṛṣṇa is the possessor of the attributes cent percent. 

And His personal expansions such as svayam-prakāśa, tad-ekātmā up to the categories of the avatāras who are all viṣṇu-tattva, possess up to ninety-three percent of these transcendental attributes. 

Lord Śiva, who is neither avatāra nor āveśa nor in between them, possesses almost eighty-four percent of the attributes.

But the jīvas, or the individual living beings in different statuses of life, possess up to the limit of seventy-eight percent of the attributes. n the conditioned state of material existence, the living being possesses these attributes in very minute quantity, varying in terms of the pious life of the living being. The most perfect of living beings is Brahmā, the supreme administrator of one universe. He possesses seventy-eight percent of the attributes in full.  

All other demigods have the same attributes in less quantity, whereas human beings possess the attributes in very minute quantity. The standard of perfection for a human being is to develop the attributes up to seventy-eight percent in full. The living being can never possess attributes like Śiva, Viṣṇu or Lord Kṛṣṇa. 

A living being can become godly by developing the seventy-eight-percent transcendental attributes in fullness, but he can never become a God like Śiva, Viṣṇu or Kṛṣṇa. He can become a Brahmā in due course. 

The godly living beings who are all residents of the planets in the spiritual sky are eternal associates of God in different spiritual planets called Hari-dhāma and Maheśa-dhāma. 

The abode of Lord Kṛṣṇa above all spiritual planets is called Kṛṣṇaloka or Goloka Vṛndāvana, and the perfected living being, by developing seventy-eight percent of the above attributes in fullness, can enter the planet of Kṛṣṇaloka after leaving the present material body." (SB, Canto I Ch 3 text 28 Purport)