The system of yoga entails controlling the mind, and the Lord of the mind is Aniruddha. It is stated that Aniruddha is four-handed, with Sudarśana cakra, conchshell, club and lotus flower. There are twenty-four forms of Viṣṇu, each differently named. Among these twenty-four forms, Saṅkarṣaṇa, Aniruddha, Pradyumna and Vāsudeva are depicted very nicely in the Caitanya-caritāmṛta, where it is stated that Aniruddha is worshiped by the yogīs. Meditation upon voidness is a modern invention of the fertile brain of some speculator. Actually the process of yoga meditation, as prescribed in this verse, should be fixed upon the form of Aniruddha. By meditating on Aniruddha one can become free from the agitation of acceptance and rejection. When one's mind is fixed upon Aniruddha, one gradually becomes God-realized; he approaches the pure status of Kṛṣṇa consciousness, which is the ultimate goal of yoga.
(Srimad Bhagavatam----3:26:28----purport).

According to the Siddhārtha-saṁhitā there are twenty-four forms of Lord Viṣṇu. First I shall describe, according to the opinion of that book, the location of the weapons, beginning with the disc.
The twenty-four forms are:
(1) Vāsudeva;
(2) Saṅkarṣaṇa;
(3) Pradyumna;
(4) Aniruddha;
(5) Keśava;
(6) Nārāyaṇa;
(7) Mādhava;
(8) Govinda;
(9) Viṣṇu;
(10) Madhusūdana;
(11) Trivikrama;
(12) Vāmana;
(13) Śrīdhara;
(14) Hṛṣīkeśa;
(15) Padmanābha;
(16) Dāmodara;
(17) Puruṣottama;
(18) Acyuta;
(19) Nṛsiṁha;
(20) Janārdana;
(21) Hari;
(22) Kṛṣṇa;
(23) Adhokṣaja and;
(24) Upendra.
(Sri Caitanya Caritamrta----2:20:223----translation and purport).

The different forms of Kṛṣṇa are distributed throughout the universe to give pleasure to the devotees. It is not that devotees are born only in India. There are devotees in all parts of the world, but they have simply forgotten their identity. These forms incarnate not only to give pleasure to the devotee but to reestablish devotional service and perform other activities which vitally concern the Supreme Personality of Godhead. Some of these forms are incarnations mentioned in the scriptures, such as the Viṣṇu incarnation, Trivikrama incarnation, Nṛsiṁha incarnation and Vāmana incarnation.
In the Siddhārtha-saṁhitā, there is a description of the twenty-four forms of Viṣṇu, and these forms are named according to the position of the symbolic representations in Their four hands. When one describes the positions of objects in the hands of the Viṣṇu mūrti, one should begin with the lower right hand then move to the upper right hand, upper left hand and, finally, to the lower left hand. In this way,
Vāsudeva may be described as being represented by mace, conch shell, disc and lotus flower;
Saṅkarṣaṇa is represented by mace, conch shell, lotus flower and disc. Similarly;
Pradyumna is represented by disc, conch shell, mace and lotus flower;
Aniruddha is represented by disc, mace, conch shell and lotus flower.
In the spiritual sky the representations of Nārāyaṇa are twenty in number and are described as follows:
Śrī Keśava (flower, conch shell, disc, mace);
Nārāyaṇa (conch, flower, mace and disc);
Śrī Mādhava (mace, disc, conch and flower);
Śrī Govinda (disc, mace, flower and conch);
Viṣṇu-mūrti (mace, flower, conch and disc);
Madhusūdana (disc, conch, flower and mace);
Trivikrama (flower, mace, disc and shell);
Śrī Vāmana (conch, disc, mace and flower);
Śrīdhara (flower, disc, mace and shell);
Hṛṣīkeśa (mace, disc, flower and conch);
Padmanābha (shell, flower, disc and mace);
Dāmodara (flower, disc, mace and shell);
Puruṣottama (disc, flower, shell and mace);
Acyuta (mace, flower, disc and shell);
Nṛsiṁha (disc, flower, mace and shell);
Janārdana (flower, disc, shell and mace);
Śrī Hari (shell, disc, flower and mace);
Śrī Kṛṣṇa (shell, mace, flower and disc);
Adhokṣaja (flower, mace, shell and disc), and;
Upendra (shell, mace, disc and flower).
(Teachings of Lord Caitanya).