Declension table of mahāmantra

Masculine	Singular	Dual	Plural
Nominative	mahāmantraḥ	mahāmantrau	mahāmantrāḥ
Vocative	mahāmantra	mahāmantrau	mahāmantrāḥ
Accusative	mahāmantram	mahāmantrau	mahāmantrān
Instrumental	mahāmantreṇa	mahāmantrābhyām	mahāmantraiḥ
Dative	mahāmantrāya	mahāmantrābhyām	mahāmantrebhyaḥ
Ablative	mahāmantrāt	mahāmantrābhyām	mahāmantrebhyaḥ
Genitive	mahāmantrasya	mahāmantrayoḥ	mahāmantrāṇām
Locative	mahāmantre	mahāmantrayoḥ	mahāmantreṣu

Compound mahāmantra -

Adverb -mahāmantram -mahāmantrāt