Monster Rancher is an anime based on a series of video games. Genki enters the monster world and, along with Holly, Mocchi, Suezo, Golem, Tiger, and Hare, searches for the legendary Phoenix, who is the only monster that can defeat the evil Moo.
Whenever a monster is killed, he or she turns into a lost disc. When Moo is destroyed, all become mystery disks and can be unlocked again, thus reviving them, except Melcarba (who is a robot and not a monster), Big Blue (who fuses with Pixie), and, in his final battle, Moo.
It is unknown how many of them were unlocked once the Phoenix turns them from a lost disc to a Mystery Disk, though a few of them are explicitly shown to be unlocked, while a few are out of reach. However, it is conceivable that all but the unreachable ones are eventually unlocked at some point, in large part due to Allan.
- Holly's grandfather - Was killed by Naga before the first episode. (as he is human he was not turned into a lost disc or revived)
- Pink Eye - Was killed by Naga before the first episode.
- Captain Black Dino - While chasing after Genki, they jumped across a ravine, but Genki got back to the side he jumped off of while Captain Black Dino fell into the raging river below.
- Black Dino troops - The two that were with Captain Black Dino fell into the raging river along with him.
- Captain Jell - Killed by Golem with a punch. (A new captain was appointed sometime after)
- Jell troops - Killed by Golem with a series of punches, saving the unfortunate Jell for last.
- Seed Sister 3 - Killed by Genki teleporting a boulder at her.,
- Worm - Killed when the two remaining Seed Sisters sucked out his energy. Was unlocked by Allan after becoming a Mystery Disk again.
- Seed Sisters 1 and 2 - Killed offscreen by Allan, presumably with his whip.
- Tiger's pack - Killed by the Dinos with their claws.
- Captain Dino - Slashed by Tiger with his claws.
- Captain Kuro - Tackled off a cliff by Ed and fell to his death in Heaven's Canyon. (Note: It is unlikely he was ever unlocked again since his disk would be at the bottom of Heaven's Canyon - if there even is one - where no one ever goes, although flying monsters could potentially find it)
- Captain Clay - Killed by Pixie with Lightning (which is sometimes misnamed as Torpedo).
- Gooji - Punched into a whirlpool by Golem
- Joker - Smashed through a wall by Hare with Dragon Kick.
- Captain Scaled Jell - Killed by Pixie with a Big Bang attack.
- Scaled Jell troops - Killed by Pixie with a Big Bang attack while fused into a cannon with their captain.
- Gali - Killed by Mocchi with the Mocchi Cannon. Was unlocked after becoming a Mystery Disk again.
- Sandy troops - Presumably killed when Gali's Gali Hurricane caused his castle to collapse. At least one was unlocked after becoming a Mystery Disk again.
- Captain Black Worm - Killed by Tiger with Lightning (misnamed as Torpedo).
- Undine - Jumped into the fire (which she caused), as Golem tried to save her but she felt she didn't deserve his friendship due to her deceiving him.
- Captain Jaggernaut - Killed by Melcarba's spin attack.
- Jaggernaut troops - Killed by Melcarba's spin attack. (earlier three were killed by him smacking them)
- Melcarba - Genki stuck a metal pole in him causing him to be struck by lightning. (Did not become a lost disc as he is a robot not a monster)
- Gray Wolf - Stabbed in the throat by Tiger with his horn. Was unlocked by Nina after becoming a Mystery Disk again.
- Cabalos - Thrown out the window of Naga's castle by Naga and fell to his death.
- Stone Dragon - Knocked into a bottomless swamp by Color Pandora with Pinwheel Fireworks and drowned. (Note: Like Captain Kuro, his disk would be out of reach even after Moo's first defeat and therefore he is unlikely to be unlocked again)
- Captain Arrowhead - Killed when Jim crashed his ship into him.
- Arrowhead troops - Killed when Jim crashed his ship into them and their captain
- Bajarl - Crushed when Holly detonated explosives causing a rock formation to fall on top of him. (Note: It is unlikely that his Mystery Disk would be recovered, but slightly possible)
- Naga - Was hanging onto the edge of his castle after being hit by the Mocchi Cannon, and let go and fell to his death. Was unlocked after becoming a Mystery Disk again.
- End Bringer - Kicked off a cliff by Genki
- Chariot - Killed by Baku in a beam struggle
- Baku - Mortally wounded by Chariot with an energy ball
- Metal Jell - Killed in explosion of factory caused by an electrical surge due to Knight Mocchi shooting at the electric devices
- Knight Mocchi troops - Killed in explosion of factory along with Metal Jell
- Evil Hare - Killed by Tiger with Lightning
- Captain Astro - Punched a wall causing a tank of water to fall and form a waterfall out of the ship and over a cliff. Captain Astro fell over the waterfall.
- Renocraft - Killed by Hare, Tiger, Golem, and Suezo with Dragon Kick, Lightning (misnamed as Torpedo), Tornado Attack, and Tail Attack.
- Captain Gangster - Stabbed in his weak point by Captain Weed.
- Captain Weed - Killed by Lilim snapping her fingers to send his Seed Machine Gun back at him.
- Lilim - Stabbed offscreen by Durahan with his broken sword.
- Evil General Durahan - Killed when his troops (who betrayed him for Moo) shot down his Iron Bird causing it to crash and explode. Was unlocked by a Weed, as a head.
- Weed messenger - Killed when Moo destroyed his castle with a breath blast.
- Durahan's troops (mostly Weeds and Jells) - Blown up inside their ships by Moo with a breath blast and dark energy sphere
- Big Blue - Fused with Pixie to turn her into Granity and heal her from her mortal injuries from her fight with Moo. (as he did not become a lost disc he was not revived)
- Moo - He and the Phoenix destroyed each other in a flash of light. His soul became trapped in the same mystery disk as Holly's father afterward, and was later fully revived to possess Durahan.
- Phoenix - He and Moo destroyed each other. The five monsters that fused into him were revived immediately after.
- Mocchi (became Mystery Disk and was unlocked)
- Suezo (immediately revived)
- Golem (immediately revived)
- Tiger (became Mystery Disk and was unlocked)
- Hare (immediately revived)
Any monsters killed in Season 3 would be revived by the Phoenix when Moo was destroyed for the second and final time, and all Baddies purified.
- Captain Jelly Gaboo - Killed by Mocchi with Mocchi Cannon
- Jelly Gaboo troops - Killed by Mocchi with Mocchi Cannon
- Mocchini - Accidentally killed by Most with Cherry Blossom Blizzard. (Set in flashback, likely before Moo's first defeat)
- Moo - Destroyed by the Phoenix (now consisting of Mocchi, Suezo, Golem, Tiger, Hare, Genki, Holly, Holly's father, Durahan, Poison, Mum Mew, Gobi, and Weed) charging into him. This is the final end of Moo, who explodes in a shower of rainbow particles.