The Something series is a Super Mario WorldRom Hack series by Yogui. The first game stars Mario and the second game stars Luigi.
Tropes in all Games
Abhorrent Admirer: The Rip Van Fish from "The Only Water Level". If they see Mario, they immediately chase him. Also, they're dreaming about finding love since they create hearts when they're sleeping.
Acrofatic: Ballser. Despite looking very round and heavy, Ballser gets faster and faster during the later phases of his boss fight. He even sprouts wings to become even faster and uses his weight to shake the ground and stun Mario.
Action Bomb: In addition to the Bob-ombs, the pink Bullet Birds, the red Bomb Boos and the dull red Yoshi Koopas explode.
Ancient Tomb: Kabu Katakomb is an Auto-Scrolling Level where Luigi has to dodge the Kabus and the bats. One section is underwater, which is difficult because Luigi is a slow swimmer and the scrolling speed is about the same as the scrolling speed of the land section.
The second half of Oldschool Temple is based on Larry's Castle.
The fourth part of the Space Hideout is based on Forest of Illusion 2, but the enemies are replaced with Thwomps and the water physics have been removed.
Cute Kitten: Cat Beach has the gimmick of collecting 75 kittens before he allows Luigi to move onto the next level. The cat even does a cute smile at Luigi when Luigi completes this task.
Collection Sidequest: Something and Something Else have sidequests where you collect 75 of the item required and the gatekeeper allows passage. Both levels have alternate exits, and thus can be skipped.
Cyclops: The Banzai Bill sprite replacement in Something.
Death Mountain: Worlds 4 and 6 in Something Else. In World 4, Luigi has to deal with Yoshis, Killer Bills, a very dark cave, and an underground mine. Luigi has to stop the invasion of the mountain village by Von Toad II and his frog cronies. In World 6, Luigi has two ways to approach the last castle. On one path, Luigi has to deal with exploding bullet birds and slippery ice blocks. On the other path, Luigi has to deal with slippery ice physics and plenty of platforming perils.
When Yoshi is hatched for the first time (most likely Happy Horse Bridge or Pipes n' P-switches) in Something, he says not to drop him in a pit. Mario does this to access either exit in Happy Horse Bridge.
One of the Athletic Peach's abilities in Something Else.
Rainy Clouds has a section where Luigi has to swim in shark-filled water and another section where the water is floating next to the clouds.
The Secret Exit route in Cat Beach in Something Else is based around this particular gimmick. One false move and Luigi plummets to his death.
Flying Face: The Yukkuri head appears as the main adversary of Yukkuri Take. It is a sprite-swap of the Angry Sun, so it can fly and mercilessly pursue Luigi.
Frogs and Toads: They appear as enemies in both games, but they are immune to fire and they ride on pogo sticks.
Fundamentally Funny Fruit: The Piranha Plants here are replaced with fruit. Jumping Piranha Plants and regular Piranha Plants are pumpkins in Something. Regular piranha plants are apples in Something Else. Venus Fire Traps are watermelons in Something Else.
The Maze of Ice Cubes in Something, which can be hard because of the ice physics.
The Mysterious Maze in Something Else. You have to find the right doors to escape the maze.
Miko: The Reimu Look-a-likes in Something Else. They are led by a Yuyuko look-a-like.
Mine Cart Madness: Mine Catastrophe. Luigi has to use Minecarts to make it to the end of the level. According to a Message Box, Luigi is dumb enough to fall through the holes between planks.
Mini Game Zone: Unlocked after beating DDDark Castle in Something Else. It lets Luigi collect lives by playing variations of the minigame played every 100 stars. There's also a secret that lets Luigi do this without playing the mini-games.
Mordor: The last world in Something. It's a dark-grey field with a Ghost House filled with ? Mushrooms, an obstacle-filled Fortress, and Ballser's Castle. Ballser is menacingly orbiting around his castle, waiting for Mario to enter.
Palm Tree Panic: World 5 in Something Else. Luigi can retrieve kitties for a giant cat, interact with mermaids, swim in floating globs of water, storm Dedede's castle, smell the flowers, climb a flower-themed tower, and fight a giant Yoshi koopa cosplayer.
Paper-Thin Disguise: The Buzzy Beetles in Something Else disguise themselves as helpful ? Orbs, but that fails since they're always moving. Also, the ? Orbs are not used as exits.
Pipe Maze: Pipes n' P-Switches, which is based around retrieving P-Switches to get rid of the coin blocks and Munchers.
Pixellation: Used to cover up the indecent act between Luigi and the Head Miko in Something Else.
Post-End Game Content: The bonus worlds in all of the Something Series. Something even advises you to complete the game before taking on the bonus world when you press the Switch Palace in World 4.
Punched Across the Room: Used as the main gimmick in Punches on Cold Ice. Mario has to be punched by the titular enemies in order to cross the massive pits.
Ratchet Scrolling: Kinder Surprise, which makes dodging the Kinder Surprise eggs much harder.
Red Eyes, Take Warning: The Banzai Bills in Something Else. They are very fast, but there are red coins that reveal their next locations.
The 3rd world in Something Else is based on Touhou Project. It also comes with a Yukkuri reference.
DDDark Castle, Kabu Katakomb and the Mysterious Maze are references to the Kirby's Dream Land series. They even use the graphics from said series. Shotzos, Kabus and Gordos are enemies in Something Else.
The Banzai Bill sprites in Something Else are based on the Magnum Bill character design from Super Mario World.
Flower Tower is a shout out to a level with the same name from Bowser's Strike Back. It even uses the same BGM.
Oldschool Temple in Something. The graphics come from the Pyramid Levels in Super Mario Bros. 2 and the Labyrinth Zone from Sonic The Hedgehog 1. The music is a remix of Marble Garden Zone Act 2 from Sonic the Hedgehog 3. The level is filled with large pits in the first half and Thwomps and spikes in the second half.
Puzzle Itemple in Something Else. To complete this optional level, Luigi has to solve the puzzles, which requires proper use of the springboards and P-Switches.
Tempting Fate: The message box in the secret area inside Dino Horse Cloud claims that there is no food in the secret area and that Luigi can't carry out the Yellow Yoshi baby through the door. Luigi proves the message box wrong by having the Yoshi baby eat the message box. Also, the Yoshi baby eats the other message boxes within the area.
The four Red Birdos in Something. Since they are Mooks, they go down very easily.
Bigeye in Something Else. He's a giant eyeball with no projectile attacks.
Weird Moon: The Evil Guy's Moon Base in Something Else. It even has an evil smirk on its face.
What the Hell, Player?: The message box at the end of Wet Weird Forest calls out Luigi if he hits it because he activated the message box layer 3 glitch and caused the Cheep-Cheeps to fall to their deaths.
Wrap Around: A Trip in A Tree is an homage to World 5-3 from Super Mario Bros. 2. It even uses enemies from Super Mario Bros. 2: the Bob-Omb and Albatoss.
Wutai: World 3 in Something Else has a distinct Japanese motif.