Greedo used the designation "Death Engine" for an Imperial war machine. This vehicle participated during the second assault wave during the attack on Nar Shaddaa's Corellian Sector in the year 1 BBY.
The Death Engine's appearance was that of a large, black vehicle, equipped with a minimum of ten blaster cannons positioned across its exterior. Two pincer-esque protrusions extended from its front, giving the impression of a gigantic crustacean hovering via its repulsorlifts. The vehicle was operated from a heavily armored command module located centrally within it.
Because Darth Vader oversaw the entire Nar Shaddaa operation, and initially planned to join the first Imperial wave, it's possible he directly commanded the Death Engine. Regardless of the commander, they displayed a complete lack of concern for non-combatant lives; the Death Engine's offensive actions resulted in the destruction of about twenty levels, causing an entire quarter of the Corellian Sector to collapse.
The "Death Engine" is not shown in the online comic adaptation of "A Hunter's Fate: Greedo's Tale." However, the text identifies the two Imperial attack vessels present at the start of the battle as disguised "Gamma Assault Shuttles", and these ships possess frontal projections that could be characterized as "crab-like." It is possible that the "Death Engine" witnessed by Greedo was simply another Gamma-class assault shuttle with modifications.