The Vancouver-lensed "Smallville" episode "Upgrade" (#9.18) , written by Andrew Landis/Julia Swift, directed by Mike Rohl, airs Friday, April 16 on the CW, featuring the return of actor Brian Austin Green ("90210") as 'Metallo'.
"...'Zod' (Callum Blue) continues to pose as 'The Blur' and asks 'Lois' (Erica Durance) to investigate a secret lab, controlled by 'Tess'' (Cassidy Freeman). An explosion rocks the lab, with Lois rescued by 'John Corben' (Green) who was a subject of multiple experiments."While investigating the explosion, 'Clark' (Tom Welling) is exposed to red 'kryptonite', taking Zod to the 'Fortress' (of Solitude). Tess turns to 'Chloe' (Allison Mack) for help and they send in Corben to stop Clark from revealing all his secrets."
Green previously portrayed 'John Corben', aka Metallo in two episodes of the ninth season of "Smallville", debuting in the episode "Savior". 
Corben is a war time reporter, who meets 'Lois Lane' and expresses his distaste for vigilantes, particularly 'The Blur" (Clark Kent).
In the following episode "Metallo", Corben is hit by a truck and wakes up with bionic additions, including a kryptonite powered matrix that replaces his heart while powering up his body.
Corben breaks out of the hospital, surging with his new implanted heart, to search for The Blur, that he blames for his sister's murder.
Corben kidnaps Lois, but Clark confronts him, trying to disable his cybernetics. When that fails, Clark heats a lead door from a nearby boiler and fixes it to Corbens chest, covering his radiating heart.
When Corben attempts to pry away the plate, he rips out his heart and dies.
Later, 'Tess Mercer' reveals she has both the kryptonite core and Corben.
Tess asks a scientist if Corben can be revived, who replies that since 'Metallo' is more machine than man, he has simply gone 'offline'...
