The first incarnation is divided into three puruṣāvatāras—namely, Mahā-Viṣṇu, Garbhodakaśāyī Viṣṇu and Kṣīrodakaśāyī Viṣṇu. Then there are the three incarnations of the modes of nature—namely, Brahmā, Viṣṇu and Maheśvara (Śiva). All the paraphernalia used in the service of the Lord is transcendental, beyond the three qualities of this material world. There is also a description of twenty-five līlā-avatāras, namely Catuḥsana (the Kumāras), Nārada, Varāha, Matsya, Yajña, Nara-nārāyaṇa Ṛṣi, Kapila, Dattātreya, Hayagrīva, Haṁsa, Pṛśnigarbha, Ṛṣabha, Pṛthu, Nṛsiṁha, Kūrma, Dhanvantari, Mohinī, Vāmana, Paraśurāma, Dāśarathi, Kṛṣṇa-dvaipāyana, Balarāma, Vāsudeva, Buddha and Kalki. There are also fourteen incarnations of Manu: Yajña, Vibhu, Satyasena, Hari, Vaikuṇṭha, Ajita, Vāmana, Sārvabhauma, Ṛṣabha, Viṣvaksena, Dharmasetu, Sudhāmā, Yogeśvara and Bṛhadbhānu.
(Sri Caitanya Caritamrta----2:1:41----purport).

A līlā-avatāra is an incarnation of the Lord who performs a variety of activities without making any special endeavor. He always has one pastime after another, all full of transcendental pleasure, and these pastimes are fully controlled by the Supreme Person. The Supreme Person is totally independent of all others in these pastimes. While teaching Sanātana Gosvāmī (Cc. Madhya 20.296–298), Śrī Caitanya Mahāprabhu pointed out that one cannot count the number of līlā-avatāras:
līlāvatāra kṛṣṇera nā yāya gaṇana
pradhāna kariyā kahi dig-daraśana
"However," the Lord told Sanātana, "I shall explain the chief līlā-avatāras."
matsya, kūrma, raghunātha, nṛsiṁha, vāmana
varāhādi—lekhā yāṅra nā yāya gaṇana
Thus the Lord's incarnations were enumerated, including Matsya, the fish incarnation; Kūrma, the tortoise; Lord Rāmacandra; Nṛsiṁhadeva; Vāmanadeva; and Varāha, the boar incarnation. Thus there are innumerable līlā-avatāras, and all of these exhibit wonderful pastimes.
(Sri Caitanya Caritamrta----2:6:99----purport).

Because almost all of these twenty-five līlā-avatāras appear in one day of Brahmā, which is called a kalpa, they are sometimes called kalpa-avatāras. Out of these, the incarnation of Haṁsa and Mohinī are not permanent, but Kapila, Dattātreya, Ṛṣabha, Dhanvantari and Vyāsa are five eternal forms, and they are more celebrated. The incarnations of the tortoise Kūrma, the fish Matsya, Nara-nārāyaṇa, Varāha, Hayaśīrṣa, Pṛśnigarbha, and Balarāma are considered to be incarnations of vaibhava. Similarly, there are three guṇa-avatāras, or incarnations of the qualitative modes of nature, and these are Brahmā, Viṣṇu and Śiva.
(Teachings of Lord Caitanya).

The supreme Manu in Vedic literature is Svāyambhuva Manu, who is an incarnation of Kṛṣṇa. All the Manus are empowered incarnations of Kṛṣṇa (manvantara-avatāra). There are fourteen Manus in one day of Brahmā, 420 in one month, all the Manus are directors of human society, ultimately Kṛṣṇa is the supreme director of human society.
(Srimad Bhagavatam---4:24:42----purport).

From this verse it can be calculated that in one month (30 days) of Brahmā’s life there are 420 manvantara-avatāras and that in one year (360 days) of his life there are 5,040 manvantara incarnations. Thus for the one hundred years of Brahmā’s life, there is a total of 504,000 manvantara-avatāras. In addition, the Manus themselves are considered partial incarnations of the Supreme Personality of Godhead.
(Sri Caitanya Caritamrta----2:20:320----purport).

Of the manvantara-avatāras, there are fourteen: (1) Yajña, (2) Vibhu, (3) Satyasena, (4) Hari, (5) Vaikuṇṭha, (6) Ajita, (7) Vāmana, (8) Sārvabhauma, (9) Ṛṣabha, (10) Viṣvaksena, (11) Dharmasetu, (12) Sudhāmā, (13) Yogeśvara, (14) Bṛhadbhānu. Out of these fourteen manvantara-avatāras, Yajña and Vāmana are also līlā-avatāras, and the rest are manvantara-avatāras. These fourteen manvantara-avatāras are also known as vaibhava-avatāras.
(Teachings of Lord Caitanya).

After describing the Līlā and guṇa-avatāras, Lord Caitanya explains the manvantara-avatāras to Sanātana Gosvāmī. He first states that there is no possibility of counting the manvantara-avatāras. In one kalpa, or one day of Brahmā, fourteen Manus are manifest. One day of Brahmā is calculated at 4 billion 320 million years, and Brahmā lives for one hundred years on this scale. Thus if fourteen Manus appear in one day of Brahmā, there are 420 Manus during one month of Brahmā, and during one year of Brahmā there are 5,040 Manus. Since Brahmā lives for one hundred of his years, it is calculated that there are 504,000 Manus manifest during the lifetime of one Brahmā. Since there are innumerable universes, no one can imagine the totality of the manvantara incarnations.
(Teachings of Lord Caitanya).

The first puruṣa is the Kāraṇodakaśāyī Viṣṇu. From His skin holes innumerable universes have sprung up. In each and every universe, the puruṣa enters as the Garbhodakaśāyī Viṣṇu. He is lying within the half of the universe which is full with the water of His body. And from the navel of Garbhodakaśāyī Viṣṇu has sprung the stem of the lotus flower, the birthplace of Brahmā, who is the father of all living beings and the master of all the demigod engineers engaged in the perfect design and working of the universal order. Within the stem of the lotus there are fourteen divisions of planetary systems, and the earthly planets are situated in the middle. Upwards there are other, better planetary systems, and the topmost system is called Brahmaloka or Satyaloka. Downwards from the earthly planetary system there are seven lower planetary systems inhabited by the asuras and similar other materialistic living beings.
From Garbhodakaśāyī Viṣṇu there is expansion of the Kṣīrodakaśāyī Viṣṇu, who is the collective Paramātmā of all living beings. He is called Hari, and from Him all incarnations within the universe are expanded.
Therefore, the conclusion is that the puruṣa-avatāra is manifested in three features—first the Kāraṇodakaśāyī who creates aggregate material ingredients in the mahat-tattva, second the Garbhodakaśāyī who enters in each and every universe, and third the Kṣīrodakaśāyī Viṣṇu who is the Paramātmā of every material object, organic or inorganic. One who knows these plenary features of the Personality of Godhead knows Godhead properly, and thus the knower becomes freed from the material conditions of birth, death, old age and disease, as it is confirmed in Bhagavad-gītā, In this śloka the subject matter of Mahā-Viṣṇu is summarized. The Mahā-Viṣṇu lies down in some part of the spiritual sky by His own free will. Thus He lies on the ocean of kāraṇa, from where He glances over His material nature, and the mahat-tattva is at once created. Thus electrified by the power of the Lord, the material nature at once creates innumerable universes, just as in due course a tree decorates itself with innumerable grown fruits. The seed of the tree is sown by the cultivator, and the tree or creeper in due course becomes manifested with so many fruits. Nothing can take place without a cause. The Kāraṇa Ocean is therefore called the Causal Ocean. Kāraṇa means "causal." We should not foolishly accept the atheistic theory of creation. The description of the atheists is given in the Bhagavad-gītā. The atheist does not believe in the creator, but he cannot give a good theory to explain the creation. Material nature has no power to create without the power of the puruṣa, just as a prakṛti, or woman, cannot produce a child without the connection of a puruṣa, or man. The puruṣa impregnates, and the prakṛti delivers. We should not expect milk from the fleshy bags on the neck of a goat, although they look like breastly nipples. Similarly, we should not expect any creative power from the material ingredients; we must believe in the power of the puruṣa, who impregnates prakṛti, or nature. Because the Lord wished to lie down in meditation, the material energy created innumerable universes at once, in each of them the Lord lay down, and thus all the planets and the different paraphernalia were created at once by the will of the Lord. The Lord has unlimited potencies, and thus He can act as He likes by perfect planning, although personally He has nothing to do. No one is greater than or equal to Him. That is the verdict of the Vedas.
(Srimad Bhagavatam---1:3:2----purport).