The Secret of Chromastone

The Secret of the Chromastone is the forty-second episode of Ben 10: Alien Force.

Plot
When Ben catches a cold, he's pleased to see Tetrax (from the original series), but is caught off guard when Tetrax demands Ben give him Chromastone. Tetrax transforms Ben into Chromastone but instead transformed into Diamondhead. Ben doesn't even have a chance to explain what happened to Chromastone when Tetrax attacks him demanding that he handed him over. Tetrax shatters Diamondhead with a weapon similar to what Vilgax uses to shatter Chromastone in Vengeance of Vilgax: Part 2 and reveals Sugilite inside. Tetrax gives Sugilite a crystal which he absorbs, then Sugilite flies off to Petropia. Tetrax soon explains about why he needs Chromastone. He tells Ben, Gwen and Kevin about Chromastone being the only one to save Petropia, by using that crystal (Sugilite's back-up) which contains a crystallized back-up of Petropia and its people (which were destroyed by Vilgax). Ben's situation gets worse when Vilgax shows up, demanding Tetrax to return the crystal Tetrax stole from him. Ben, Gwen, Kevin and Tetrax fight Vilgax until Kevin accidentally tells Vilgax what's going on when our heroes and Tetrax tried hiding in a secret warehouse in the sewer (which Gwen thinks is disgusting and stupid) but Vilgax finds them because of Ben's sneeze echoing throughout the warehouse. Vilgax flies to Petropia, while Ben, Tetrax, Gwen and Kevin go aboard Tetrax's ship and fly to Petropia. Vilgax soon arrives to Petropia and fights Sugilite, demanding he returns the crystal. Sugilite pleads for mercy, but Vilgax reveals he has none. Ben, Gwen, Kevin and Tetrax arrives to Petropia, in order to protect Sugilite. Vilgax plucks the crystal off Sugilite, only to discover the crystal's power had been used up, throws it away and flies back to Vilgaxia. A dying Sugilite hands Ben a second crystallized back-up before fading away. Ben then turns into Diamondhead (revealing that Diamondhead knows what to do with the crystal) and climbs to the top of Petropia to revive Petropia's people. Diamondhead's actions revive both the Petrosapiens and Sugilite, who reveals to Ben that he is Sugilite, Guardian of Petropia and reveals that Chromastone still remains within the Omnitrix. Tetrax later flies Ben, Gwen and Kevin down to Earth. Meanwhile, Vilgax catches Ben's cold.

Major events

 * Tetrax returns and seeks help from Ben.
 * Sugilite is released from Diamondhead.
 * Ben revives Petropia and the Petrosapiens.

Characters

 * Ben Tennyson (sick)
 * Gwen Tennyson
 * Kevin Levin
 * Tetrax
 * Sugilite
 * Resurrected Petrosapiens

Villains

 * Vilgax (sick at the end)
 * Psyphon (cameo)

Aliens Used

 * Diamondhead (sick; 2x)
 * Humungousaur (sick; accidental transformation; selected alien was Way Big)
 * Jetray (sick)
 * Echo Echo (sick)

Errors

 * When Tetrax said fall back and regroup, Kevin's body was reciprocated twice.
 * When Sugilite is talking to Ben at the end, he says "I am in your debt, as are all Crystalsapiens", instead of Petrosapiens. However; according to Dwayne McDuffie, Sugilite "knows a secret".
 * All of the Petrosapiens in the crowd appear to be adult males, and have Chromastone's body texture.

Trivia

 * Due to the animation differences from Ben 10, many changes have been made to one particular scene: Tetrax witnessing the destruction of his home planet.
 * When Diamondhead revived the Petrosapiens, no female or child Petrosapiens were seen.
 * It is revealed that Chromastone can fly.
 * Unlike Side Effects, Ben's alien transformations didn't have their powers affected. However, the aliens were weaker than normal.