The story starts as Vilgax invades Bellwood with a gigantic Null Void Projector releasing hundreds of Null Void Prisoners into the city. Ben attempts to transform into Alien X, but Professor Paradox stops him stating that now is not the right time to use Alien X. Instead they split up to tackle the invasion. Ben fights his way to Psyphon (who's coordinating the attack from ground level), when Ben defeats Psyphon he brings to life a Mr. Smoothy sign as a distraction. Ben defeats Mr. Smoothy by quickly hitting it with every alien in his arsenal except for Cannonbolt and Alien X in the process putting the Omnitrix into reboot mode and locking out most of Ben's arsenal. To make matters worst, Professor Paradox informs the trio that Vilgax has taken over Earth so he sends them back far enough in time to destroy every power source for his Null Void Projector possible in the whole galaxy stating that the first is being recycled from the toxic radioactive waste of Vulpin: Wildmutt's home planet, however only Spidermonkey, Big Chill, Humungousaur, Swampfire and Cannonbolt are availible.
Arriving on Vulpin, Ben orders Gwen, Kevin, and Ship to stay put, because if Vilgax arrives it will take all of them combined to hold him off. Ben fights his way throughout the refinery, going through Vilgax's bioids, the local Vulpimancers and a giant two-headed snake. Ben then finds the Vreedle Brothers and manages to defeat them. Then, Ben finds a holographic message from Max stating that the one Ben destroyed isn't the only one and states that he's currently on his way to Terradino: Humungousaur's home planet, to destroy the energy core there. Goop is then unlocked.
Arriving on Terradino they find another message from Max stating that the energy core is located in the nearby temple and that Vilgax's forces are all ready there. Ben once again orders his companions to stay and hold off Vilgax if he shows up. Traveling through the temple Ben solves complex building sized puzzles and fights off not only Vilgax's droids, but also Charmcaster's rock monsters. Ben confronts Charmcaster inside the temple and despite Charmcaster using the temple's complex defences to her advantage, Ben is ultimately the victor. Ben successfully destroys the energy core, thus destroying the temple. The trio finds another message from Max stating that the next energy core is on Encephalonus IV: Brainstorm's home planet, and that one of Ben's old enemies is there but due to a glitchy transmission could not specify which one. Brainstorm is then unlocked.
Arriving on Encephalonus IV, Ben has already watched Max's message 12 times but is still unable to decipher whom Max was talking about. Kevin and Gwen stay with Ship in order to fend off Vilgax if need be. Brainstorm is unlocked here. After making his way through Encephalonus IV's complex security system and Vilgax's droids who have already arrived on the planet, Ben discovers that Darkstar is also after the energy core (likely intending on absorbing it's energy). Ben successfully defeats Darkstar and destroys the energy core. He receives a message from Max stating that the last energy core in the known universe is on Anur Phaetos: Ghostfreak's home planet, however the transmission is interrupted by Vilgax who mocks Ben by stating that he won't even be able to find the planet let alone survive it. Echo Echo is then unlocked
It appears that Vilgax's mockery holds true, Anur Phaetos is not a planet in the technical sense but in fact a alternate dimension one of which they can't access. Then, out of the blue Verdona arrives and states that Max sent her to help. She transports the trio to the Anur Dimension but she accidentally splits them up. Echo Echo is unlocked here. To make matters worst Zs'Skayr is revealed to be "alive" and well and states that Ben was most unwise to travel into his domain. After defeating Zs'Skayr's ectonurites, Ben confronts Zs'Skayr himself and defeats him by taking full advantage of his only weakness: light. Gwen, Kevin and Ship find Ben by tracking his mana but sadly Gwen isn't able to find Verdona. Paradox arrives and sends them back to their own dimension, he states that Max knew his transmissions were being interrupted and attempted to deceive Vilgax. While all energy cores have been destroyed Vilgax has someone under his employment making a new one from the energy in Taedenite on Mor' Otesi: Chromastone's home planet. Chromastone is then unlocked
The trio arrives on Mor' Otesi, and are shocked to discover that Vilgax's mysterious accomplace is none other than Cooper. Realizing he's been tricked, and that his research is going to allow Vilgax to conquer the earth, he formulates a plan to help and directs Ben to the scientific research center where all the Taedenite and his equipment is being kept. Chromastone is unlocked here. After fighting through the radioactive planet, Ben discovers a second accomplace to Vilgax's plot: Albedo. After defeating Albedo, Ben destroys the energy core Albedo had only just completed. Gwen and Kevin arrive and state that Cooper was able to by pass the security system to let them in. They also meet up with Max in the flesh. Max remorcefully tells them that while they did destroy all the energy cores there is one left and if Vilgax gets his hands on it the whole mess is on him. Jetray is then unlocked
Max states that the final energy core is among his stash of tech from when he was known as "The Wrench" in the Null Void. The last form, Jetray, is unlocked here. He reveals that he has a get out of jail free card if you will, a extremely rare device known as a skeleton key level 12 tech capable of transporting anyone back and forth into the Void. However it only has enough power for one person and Ben will need the final energy core intact in order to get back home. Ben enters the void and defeats the rather prominen forces of Vilgax. While making his way to Max's old hideout, he discovers that D'Void is now living in the hideout and aided by two Null Guardians, he fights Ben. Ben is able to defeat D'Void by destroying his Kormite generators as Big Chill. He retrieves the final core as well as a portrait of himself, Gwen and Max from the summer Ben found the Omnitrix. Ben discovers that despite all the time he spent in the Void, virtually no time has went by in the main dimension.
The team arrives back in Bellwood in the middle of the invasion but without any of the energy cores, Vilgax's projector has run out of power. The only thing left to do now is clean up the mess Vilgax made. Max states to let him and the others finish off Vilgax's droids and Null Void beasts and orders Ben to go after Vilgax. After defeating three of the toughest brawlers in the Null Void, Ben is beamed aboard Vilgax's ship for a final showdown. After defeating Vilgax, the final energy core is taken by Psyphon, who attempts to use it to fry Ben with raw Null Void energy. Paradox freezes time for all except himself and Ben and states that now is the right time to use Alien X. Ben complies and convinces Serena and Bellicus that unless they stop them Psyphon and Vilgax will destroy them. Alien X redirects Psyphon's portal so it sucks up Vilgax, Psyphon and the ship. Ben arrives on ground level and turns back to normal. Azmuth arrives and rewards Ben by unlocking a new feature in the Omnitrix.
Vilgax: (laughs) And now, at long last, the Earth will be mine! Psyphon, power up the Null Void projector!
Psyphon: Yes, Vilgax. Yes, Vilgax. Your magnificence, your... your, big and scariness. (Psyphon presses a red button, unleashing more drones and beasts)
Vilgax: Psyphon! Go manage the ground battle!
Psyphon: Already on my way, sir. (flies off in his ship)
Vilgax: Psyphon, take some backup with you!
Psyphon: Done, sir. (a few other pods follow him)
Vilgax: And Psyphon, one more thing while you're down there; bring me the head of Ben Tennyson!
Psyphon: (crashes his ship and comes out wounded) I meant to do that. You heard Vilgax! Spread out! Find Ben Tennyson!
(Meanwhile, Ben's team is watching)
Ben: Looks like it's hero time. (dials through the Omnitrix, looking for Alien X when Paradox appears and stops him)
Ben: Professor Paradox!
Paradox: Greetings, all. Good to see you again. Or should I say, in the future it would have been good to have seen you before! (sighs) Time travel can make verb tenses so very confusing. When are we, now, anyway?
Ben: Vilgax is invading the Earth.
Paradox: Ah, splendid. Then I did arrive in time to warn you that now is not the right time to use Alien X.
Ben: What? Then what should I...? (Paradox vanishes) - Professor? Where did he go?
Gwen: You mean, when did he go.
Kevin: Does it matter? Vilgax is still invading!
Gwen: We've got to do something.
Kevin: Anytime, now, Tennyson.
Ben: We'll be able to defend more ground if we split up. Go! (Gwen and Kevin run off, Ben clicks the Omnitrix, and level 1 begins)
For the most part, gameplay across the seven included worlds is a balance of action and puzzle-solving that revolves around the skills of Ben's alien forms. For example, Ben might need to change into his Humongousaur form to break through doors, or use his Swampfire form to ignite flammable substances. Each form has different combinations and special attacks that it can execute, and Ben can unlock new abilities by defeating enemies and collecting glowing energy orbs. However, there is one gameplay element that players should be aware of: using a form's innate abilities drains energy from Ben's Omnitrix meter, preventing them from continually being used until the meter can recharge. As a result, players will need to focus on combos and save their special attacks for finishing blows instead of constantly wielding them in battle.
This game is based off season three of Alien Force, due to the fact that it contains the returns of villains that haven't been seen since the original show such as Charmcaster and Zs'Skayr, and returns of Alien Force villains like the VreedleBrother, Darkstar, Albedo, and Vilgax.
Vilgax was sent to Null Void with his Ship in Ben 10: Protector of Earth and he is also sent Null Void with his ship in this game.
In the elevator in Bellwood, the tune from the original series theme song can be heard as elevator music.
This is the first Ben 10 video game that doesn't have Kevin as a boss.
In the game, Gwen and Kevin are still in their season 1-2 clothes
The makers of the game made an animation mistake on Chromastone and Cannonbolt . In the show, he has six crystals on his back and Cannonbolt has an extra line on his back shell, while in this game, Chromastone only has four and Cannonbolt has one less. The Chromastone error was fixed on the DS.
In the game, Alien X has black hands instead of white.
This video game became the best-selling video game (Platinum-The best of PSP)
In the game, when the aliens say their names, the sound the same way they do on the Ultimate Omnitrix toy. Except for Cannonbolt who sounds they way he did in the original Ben 10 episode, Game Over when he said after getting the Cannonbolt icon, "Cannonbolt style!".
The DS version of the game was referenced in the Ultimate Alien episode Ben 10,000 Returns referring specifically that, in an alternate timeline, Albedo was trapped in the form of Alien X for a year (which would have been prevented in the Main stream timeline by the fail safe Ben had Kevin put on the Omnitrix).
This game has a gameplay similar to Ristar, in which the main hero goes to six planets (not counting Earth) and battles villains before fighting the main villain, who wants power and to conquer the universe.
This is the first time we see Vilgax use his ray gun.