siddha-amṛta-rasa-spṛṣṭāḥ - the demons, thus being touched by the powerful mystic nectarean liquid; vajra-sārāḥ - their bodies becoming invincible to thunderbolts; mahā-ojasaḥ - being extremely strong; uttasthuḥ - again got up; megha-dalanāḥ - that which goes through the clouds; vaidyutāḥ - lightning (which penetrates the clouds); iva - like; vahnayaḥ - fiery.

When the dead bodies of the demons came in touch with the nectar, their bodies became invincible to thunderbolts. Endowed with great strength, they got up like lightning penetrating clouds.