Death rains from above - Airburst Rockets. After about 60 yards the main rocket explodes, releasing six more smaller rockets downwards.
For technical details regarding this item see: Mechanics
Nidhogg is the name of the mighty Dragon of Death from Norse mythology, who constantly gnaws at the roots of the world-tree Yggdrasil. It is told that Nidhogg exists even beyond Ragnarök (twilight of the gods) to collect the corpses of the fallen and take them to the underworld.