Declension table of mahāmantra

Neuter	Singular	Dual	Plural
Nominative	mahāmantram	mahāmantre	mahāmantrāṇi
Vocative	mahāmantra	mahāmantre	mahāmantrāṇi
Accusative	mahāmantram	mahāmantre	mahāmantrāṇi
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