SB 1.3 - Various types of incarnations
There are various incarnations like the līlā incarnations of Matsya, Kūrma Varāha, Nṛsiṁha, Vāmana and others. Then there are guṇa incarnations of Brahmā, Viṣṇu and Śiva. Lord Viṣṇu is non different from the Personality of Godhead. Lord Śiva is in the marginal position between the Personality of Godhead and the jīva. Brahmā is always a jīva-tattva. The highest pious living being is empowered with the potency of the Lord for creation, and he is called Brahmā. When there is no such qualified living being, the Lord Himself becomes a Brahmā. Lord Śiva is the plenary portion of the Lord, but because he is in direct touch with material nature, he is not exactly in the same transcendental position as Lord Viṣṇu. The difference between Śiva and Viṣṇu is like that between curd and milk. Curd is nothing but milk, and yet it cannot be used in place of milk.
The next incarnations are the Manus. Within one day of Brahmā there are 14 Manus. Thus there are 14 times 30 times 12 times 100 (504,000) Manus in the duration of Brahmā’s life. There are innumerable universes, with one Brahmā in each of them, and all of them are created and annihilated during the breathing time of the puruṣa. Some of the prominent Manus are: Svāyambhuva Manu, Svārociṣa Manu, Vaivasvata Manu (the present Manu) etc.
Then there are the yuga-avatāras, or the incarnations of the millennia, who each possesses a different color. The colors of the incarnations in Satya, Tretā, Dvāpara and Kali yugas are respectively white, red, black (Kṛṣṇa) and yellow (Caitanya). All incarnations are mentioned in the scriptures and no impostor can be an incarnation. Apart from the direct incarnations of the Lord there are empowered incarnations. When they are directly empowered they are called incarnations, but when they are indirectly empowered they are called vibhūtis. Directly empowered incarnations are the Kumāras, Nārada, Pṛthu, Śeṣa, Ananta etc. The vibhūtis are described in the Bhagavad gītā.