Ratadrabik of Urborg and Leyline of Singularity on the battlefield.
({1} magic symbol) available.
Steps
Cast Phyrexian Dreadnought by paying ({1} magic symbol) .
When Phyrexian Dreadnought enters the battlefield, it triggers, causing you to sacrifice it.
When Phyrexian Dreadnought dies, Ratadrabik of Urborg triggers, creating a token copy of Phyrexian Dreadnought that is a 2/2 Zombie, and that is legendary due to Leyline of Singularity.