Author's Note: Here is a guide to all aliens that Rook has unlocked as well as alternate dimension Bens. Note that they are not canon lists.
I am including Prime, 23, No Watch, Mad, Bad, Zarro, and Nega as well as Gwen 10, Argit 10, and Reboot Ben (instead of OS Ben). Not all of them will be very present for the story though. Also, note that some Bens have aliens that Prime doesn't so they may be unfamiliar such as Trunkman and The Darkness.
Most alternate Bens have access to all the same aliens as Prime, except 23. I am listing all the aliens Prime has but for alternate Bens who have an unknown number of total aliens, I am only listing ones with unique names and non-canon aliens that I wanted to give the Bens. When "others" is listed, assume the Ben has access to more of Prime's aliens. Also, in the story not all Bens will call their aliens by names but I will refer to them by Prime's names for them to avoid confusion.
There are no fanmade aliens here but I did give names to canon aliens/ transformations including Tidetail Wave (dolphin), Pumpkin King (Anur Transyl mutant pumpkins), Night Mare (ghost horse seen in The Most Dangerous Game), Acrocat (transformation of a Revonnahgander), Sabertooth (Ditto's predator), Dez (Zed's species), and Starfire (Tamaranean, which is from DC comics but confirmed to exist in Gwen 10's universe).
The rest are canon or were designed/ named by creators offscreen or aliens that appeared in commercials but not the show. Those aliens include Archfiend (Archfiendzarro in canon, as it was introduced for Benzarro), Terrorsaur, Antigravitesla, Kringl the Summoner, Moot (Highbreed), Brain Drain, L'Goon, Skele-TON, Snorcupine, Alien Z, Transmutor, Snakepit, Jak, and Snark Tanque.
Rook Blonko (Omnitrix): Tidaltail Wave (dolphin), Archfiend, Antigravitesla, Terrorsaur, Four Arms, Juryrigg, XLR8, Bloxx, Kringl, Wildvine, Diamondhead, Upgrade, Shockrock, Crashhopper, Funguy, Moot, Lodestar, Rath, Slapback, Warp, Snare-Oh, Blitzwolfer, Ghostfreak, Whampire, Frankenstrike, Pumpkin King, Brain Drain, Night Mare, L'Goon, Skele-TON
Ben Prime (Omnitrix): Heatblast, Wildmutt, Diamondhead, XLR8, Grey Matter, Four Arms, Stinkfly, Ripjaws, Upgrade, Ghostfreak, Cannonbolt, Wildvine, Blitzwolfer, Snare-Oh, Frakenstrike, Waybig, Upchuck, Ditto, Eye Guy, Swampfire (blossomed), Echo Echo, Humungousaur, Jetray, Big Chill, Chromastone, Brainstorm, Spidermonkey, Goop, Alien X, Lodestar, Rath, Nanomech, Water Hazard, AmpFibian, Armodrillo, Terraspin, NRG, Fasstrack, Clockwork, ChamAlien, Shocksquatch, Eatle, Jury Rigg, Feedback, Bloxx, Gravattack, Crashhopper, Ball Weevil, Walkatrout, Pesky Dust, Molestache, The Worst, Kickin Hawk, Astrodactyl, Whampire, Bullfrag, Gutrot, Buzzshock, Articguana, Toepick, Atomix
Ben 23 (Hero Watch): Freeze Lizard (Articguana), Charcoal Man (Heatblast), Mr. Monkey (Spidermonkey), Plug Man (Feedback), Vomit Man (Upchuck), Rollaway (Cannonbolt), Electric Yeti (Shocksquatch), Orbit Man (Gravattack), Fright Face (Toepick), Dognabbit (Wildmutt), Handy-Man (Four Arms), Brain Frog (Gray Matter), Speedyquick (XLR8), Techno-Bubble (Upgrade), Fish Fingers (Ripjaws), Big Bug (Stinkfly), Acrocat (Revonnahgander), Mr. Mucky (Swampfire), Dino-Mighty (Humungousaur), Nighty Knight (Pesky Dust), Windy-Hindy (Clockwork), Build-A-Guy (Bloxx), Trunkman (Trombipulor's species)
Rook 23 (Nemetrix): Buglizard (Stinkfly's predator), Crabdozer (Heatblast's predator), Hypnolick (Big Chill's predator), Mucilator (Crashhopper's predator), Omnivoracious (Gray Matter's predator), Slamworm (Armodrillo's predator), Terroranchula (Ball Weevil's predator), Tyrannopede (Humungosaur's predator), Vicetopus (Brainstorm's predator), Sabertooth (Ditto's predator), Dez (Zed's species), various Earth predators
No Watch (None): same as whoever's Omnitrix he is wearing
Mad Ben (Power Watch): Snorcupine, Transmutor, Snakepit, Plantapocolypse, others
Bad Ben (Omnitrix): Shockrock, Snakepit, Jak, Snark Tanque, others
Benzarro (Zombitrix): Spitterzarro, Archfiendzarro, Brain Drainzarro, others
Nega Ben: The Darkness, The Electric Corpse (Frankenstrike), others
Gwen 10 (Gweniverse Omnitrix): Canonbolt, Diamondhead, Goop, Stinkfly, Upgrade, Wildmutt, Wildvine, XLR8, Starfire (Tamaranean), Alien Z
Argit 10 (Argitrix with Master Control): Human (unnamed), others
Reboot Ben (Omnitrix): Overflow, Shockrock, Slapback, Jetray, Humungousaur, XLR8, Diamondhead, Heatblast, Wildvine, Cannonbolt
