|Home world:||Yapool's Dimension|
|First Appearance:||Ultraman Mebius & the Ultra Brothers|
|Latest Appearance:||Mega Monster Rush Ultra Frontier|
U-Killersaurus (Uキラーザウルス U-Kirāzaurusu) is a powerful choju, probably among Yapool's strongest, it later evolves into U-Killersaurus Neo (Uキラーザウルス・ネオ U-Kirāzaurusu Neo). It first appeared in the film, Ultraman Mebius & the Ultra Brothers.
- U-Killersaurus: Ultimate Choju (究極超獣 Kyūkyoku Chōju)
- U-Killersaurus Neo: Ultimate Giant Choju (究極巨大超獣 Kyūkyoku Kyodai Chōju)
Ultraman Mebius & the Ultra Brothers
First Battle Against the Ultra Warriors
At the beginning of the movie, U-Killersaurus is seen fighting against the Ultra Brothers; Ace, Ultraman, Ultraseven, and Jack on the Moon. However, U-Killersaurus is able to overpower the four Ultra Brothers with its strength. When the Ultra Brothers combined their beams into one, U-Killersaurus takes flight and dodges their combination beam and flys towards the Earth. While fighting on space, as the Ultras tried to use their Ultra Beams, Ultraman warned them if it misses, it will directly hit Earth. As a result, U-Killersaurus took the chance and grab the Ultras with his tentacles until Ultraman uses his Ultra-Slash to free them. After Ultraman and Seven weakened the Choju, Ace and Jack blast it down towards the sea of Earth with their Metallium Ray and Specium Ray respectively. The four Ultra Brothers then sealed Yapool and U-Killersaurus with their Final Cross Shield.
Revival and Destruction
"Why would you, towards a friend--"
"A friend? Don't make me laugh."
- ―Yapool, as U-Killersaurus, reveals to Mebius that he's been using Alien Nackle as a pawn
Twenty years later, the seal of U-Killersaurus become undone thanks to Alien Guts and Alien Nackle. Yapool revived as well, later U-Killersaurus killed Alien Nackle, which is supposedly their ally but Yapool revealed they are nothing than just pawns. The Choju then proceeds to evolve into U-Killersaurus and overpowers the Ultra Brothers and Mebius. Until Taro and Zoffy arrival to restore the energies of the Ultras, they managed to fight on par with the Choju by using their beams and slash attacks. When Mebius about to use his Mebium Shoot, the Choju (Yapool) shows that he held Aya hostages and then blasted the latter with his Killer Eye Ray and holding Mebius on the ground with mandibles and prepares to use his ultimate attack on Mebius. Though suceeded in using his ultimate attack, the Ultra Brothers then fuses with Mebius and transforms into Mebius Infinity. U-Killersaurus Neo then crumbled to dust after Mebius Infinity uses his Cosmos Miracle Attack and dashing into his body and saving Aya.
- U-Killersaurus's roar was later reused for King Pandon.
- According to the final cutscene of Ultraman Fighting Evolution 0, its full name is Ultra-Killersaurus (ウルトラキラーザウルス Urutora-Kirāzaurusu).
- Height: 79 m
- Weight: 82,000 t
- Powers and Weapons
- Electric Blasts: U-Killersaurus can fire purple electric blasts from an unknown part of his body.
- Saurus-Stinger: The spikes on U-Killersaurus' back can launch out and zoom around multiple enemies before exploding. Each missile is basic in power, but the sheer number of them make this a devastating attack.
- Terrible Flasher: U-Killersaurus can emit a flash of bright light from the purple orbs on his chest and shoulders. This flash can stun his opponents for a short period of time while also making them flinch. It can also push his opponents back several yards.
- Clawed Tentacles: U-Killersaurus is equipped with numerous tentacles that can extend several hundred, possibly thousand, feets. While these tentacles can ensnare and bash opponents, each is also tipped in claws that are perfect for gripping struggling opponents.
- Boosters: U-Killersaurus has rocket boosters on his back. This allows him to fly at great speeds, even in space.
- Evolution: After its revival, U-Killersaurus is able to evolve into its Neo form.
- Height: 303 m
- Weight: 939,000 t
- Powers and Weapons
- Clawed Tentacles: In addition to its original tentacles, U-Killersaurus is equipped with several more on its back.
- Feeler Shock: U-Killersaurus Neo can fire a red beam of energy from his tentacles. This beam is strong enough to virtually destroy nearly any opponent in one hit.
- Killer Eye Ray (キラーアイレイ Kirā Ai Rei): When needed, U-Killersaurus Neo can fire beams of blue energy from his eyes. The exact strength of these beams is unknown.
- Dynamite Eraser (ダイナマイト・イレイサー Dainamaito Ireisā): U-Killersaurus Neo is equipped with a powerful energy cannon on its belly. This cannon can fire a beam of energy of unknown strength.
- Saurus Full Burst (ザウルス・フルバースト Zaurusu Furu Bāsuto): U-Killersaurus Neo's strongest attack, the death beam is fired from between its mandibles and can virtually vaporize the strongest of opponents in a single hit. If his mandibles aren't out of the way when fired, they will also be completely vaporized.
- Killer Warheads (キラー・ウォーヘッド Kirā Uōheddo): U-Killersaurus is able to fire the larger spikes on its side, in addition to its original spikes.
- Mandibles: U-Killersaurus Neo has a very large set of powerful, crushing mandibles on the front half of his body.
- Origin: Unknown planet where Plasma Verokron was destroyed
- Powers and Weapons
- Flight: Plasma Killersaurus can travel through space at his leisure.
- Plasma Soul Generation: It is unknown if it actually created the substance or if the pieces just fell of, but the planet sized monster caused the spread of the mineral Plasma Soul and the appearance of more Plasma Monsters.
- Endurance: Though not specifically stated but, due to the fact that it is a mutated U-Killersaurus and that it survived the crushing weight and height of a planet's innards. It is assumed Plasma Killersaurus hold great durability and/or resistance.
Mega Monster Rush Ultra Frontier
U Killersaurus returns as Plasma Killersaurus (プラズマキラーザウルス Purazuma Kirāzaurusu) in Mega Monster Rush Ultra Frontier VEROKRON Hunting. After defeating Plasma Verokron, the Rush Hunters returned to the Hunter Station while greeted by a cheering crowd. However they then witnessed the destruction of the planet they were fighting on, discovering that it was the home of Plasma Killersaurus. The titanic beast took of through the cosmos, spreading Plasma Soul around the cosmos and the appearance of more Plasma Monsters.
Plasma Killersaurus Hunting
Baltan Battler Barel, Guts Gunner Garm, and Magma Master Magna were secretly went to a planet filled with lava and a surface just like our Moon to find and hunt Plasma Killersaurus. Shortly after discovering it hiding, the monster woke up. The trio then ran to avoid chunks of fallen stalagmite until they stopped, discussing how Killersaurus came to this planet and how to get the monster's Plasma Souls. When the creature fully awoken, the trio endured a sandstorm, that was followed by the monster's roar and leaped high to dodge an attack. After dodging the creature's lightning bolt attack, the trio decided to attack it. Garm decided to fire his Gatling Shots at the behemoth, but it protected itself with an energy shield. Barel then launched his Lightning Boomerang at the creature, but it absorbed it into his body. Magna then summoned his Lightning Claw to attack, but the monster launched a plasma ring to knock him out of the air. He tried again, but this time, he saw a vision of a new sword before dodging another of Killersaurus's attacks. When the creature fired his lighting again, Magna deflected it, but at the price of his own weapon. Magna then retreated and was joined by the others. Killersaurus fired another lightning weapon at them, but this time, Garm countered it with his Gatling Gun. Unfortunately, he too lost his weapon afterwards. Magna then summoned his inner power and charged straight at the beast resulting in a small explosion. He may have been knocked back, but, he gained a new sword in the process. After a few moments of discussion, Magna summoned the power of the weapon, lighting it up and striking a major part of Killersaurus's Plasma Souls, and soon after, it left, but not without Magna losing his new sword.