mano-vīrya-varotsiktam
asṛṇyam akuto-bhayam
bhÄ«tÄ nililyire devÄs
tÄrká¹£ya-trastÄ ivÄhayaḥ
manaḥ-vÄ«rya - by mental and bodily strength; vara - by the boon; utsiktam - proud; asṛṇyam - not able to be checked; akutaḥ-bhayam - fearing no one; bhÄ«tÄḥ - frightened; nililyire - hid themselves; devÄḥ - the demigods; tÄrká¹£ya - Garuá¸a; trastÄḥ - frightened of; iva - like; ahayaḥ - snakes.
The asuras are generally strongly built, as described here, and therefore their mental condition is very sound, and their prowess is also extraordinary. HiraṇyÄká¹£a and HiraṇyakaÅ›ipu, having received the boon that they would not be killed by any other living entity within this universe, were almost immortal, and thus they were completely fearless.