Dragon Ball Super's Sneak Peek preview for episode 21 titled 'The Revenge Begins! The Frieza Army's Malice Strikes Gohan!' shows that Frieza's army is one hour away from landing on earth. According to the synopsis for Dragon Ball Super episode 21, Bulma is going to attempt get Jaco's message to Whis, who is training with Goku and Vegeta but unexpected events stopping Bulma from delivering the message.

Dragon Ball Super has been hugely successfully for the past four months since its debut on July 5, but the earth is imperiled. According to the trailer, Frieza and his army will land on Earth in just an hour.

Dragon Ball Super has been following the Resurrection F saga starting after the end of the Battle of Gods saga. Goku transformed into a Super Saiyan God to take on the God of Destruction Belarus. While there was no clear winner, it taught Goku it was time to take training from Whis.

Fuji TV broadcast episode 20, titled "Warning from Jaco! Frieza and his 1,000 Soldiers are Drawing Near!" on November 22. Attack of the Fanboy reported that Frieza is preparing for his arrival on Earth. The sneak peek also showed a glimpse of the Super Saiyan Blue form that Goku and Vegeta take when they fight.

Jaco arrived on Earth to warn that Frieza and his army are hours away from invasion. The Z fighters take arms against Frieza. Attack of the Fanboy warned that most of the episode is "recycled" and "redundant."

In Dragon Ball Super episode 21 titled, "The Revenge Begins! The Frieza Army's Malice Strikes Gohan!"we will see the battle between the Frieza's army and Z fighters.

The Dragon Ball Super episode 21 preview from Toei Animation shows Frieza and his 1000-strong army landing on Earth and the five Z fighters getting ready to battle.

Another clip shows Goku and Vegeta finishing their training from Whis. The trailer also shows Goten and Trunks playfully trying to figure out how Jaco works. They assume the intergalactic patrolman is a toy.

Yibada warns that fans should be ready to see a huge battle in the upcoming episode.

Frieza doesn't seem interested in a battle with Piccolo and Gohan. He orders his army to attack Kuririn first.

"Dragon Ball Super" Episode 21 airs Sunday, Nov. 29, 2015.