There's a 1v1 hazards-off tournament going on here:
https://www.youtube.com/watch?v=zjME4R9H_G8
Known so far from the stream and twitter people who saw other matches at the same event:
Pokemon Stadium: No transformations
Super Happy Tree: Still has the clouds.
Duck Hunt: No ducks/dog
Reset Bomb Forest: No transformations
Warioware: No transformations
Delfino Plaza: Still transforms
Hyrule Castle: No tornadoes
Mute City SNES: Static layout, ground still hurts you
Yoshi's Island: Middle platform doesn't tilt, no Shy Guys or Whimsical Support Ghost
Mushroom Kingdom: No change (???)
Living Room: No change (???)
Green Greens: No blocks/bomb blocks, no mention of Whispy Woods and apples
Jungle Japes: No Klaptrap, water still carries you offscreen
Unova Pokemon League: Flat + 2 platforms, Pokemon appear but do nothing
Dream Land: No wind
Boxing Ring: No change
Suzaku Castle: No change
Castle Siege: No transformations
Norfair: No lava
Figure-8 Circuit: No karts
Saffron City: No Pokemon
Town & City: No balloons, platforms do not move all the way to blast zone
Princess Peach's Castle: No Banzai Bill, no buttons for platforms, existing platforms static
Umbra Clock Tower: No platforms
Wily Castle: No platforms, no Yellow Devil
Distant Planet: Leaf platforms don't sink under player weight, no rain, no Bulborb, no pill flowers
Paper Mario: No transformations, no desk fan blowing wind
Tomodachi Life: No change
Dracula's Caste: "Static and good"
Kongo Falls: Rock still exists, stage doesn't sink under player weight, no logs getting stuck in waterfall
Bridge of Eldin: No King Bulblin or bomb
Mario Circuit: Still transforms, no Shy Guys, background is still dangerous
Moray Towers: No change
Skyloft: No transformations
Luigi's Mansion: Pillars can't be hit
Mushroom Kingdom U: No transformations
Frigate Orpheon: No fllipping
Golden Plains: No coins
Brinstar: Stage elements are indestructible, no acid
Gerudo Valley: Indestructible bridge, no Twinrova
Spirit Tracks: "Stage doesn't move at all" (relative to screen or tracks?), platforms sometimes float overhead
Shadow Moses Island: Indestructible walls
Coliseum: No platforms (
boring...)
Wii Fit Studio: Two static platforms
The Summit: Still transforms, no fish, ice is unbreakable
Brinstar Depths: No Kraid, therefore static
Rainbow Cruise: Static stage, just the ship
Halberd: Combo Cannon does not attack, otherwise no change
Fountain of Dreams: Platforms are static
Pokemon Stadium 2: No transformations
3D Land: No spikes, otherwise no change
Smashville: Platform is static, no balloons
Wuhu Island: No transformations
Port Town Aero Dive: No racers, track is still dangerous when flying around
Kalos Pokemon League: No transformations
Arena Ferox: Starts at and remains in statues transformation
Pilotwings: Red plane only, background is still dangerous
Pirate Ship: No catapult, tornado, bombs, shipwreck, King of Red Lions, tilting
Corneria: No Arwings or laser
Venom: No Arwings
Final Destination: No change lol
Yoshi's Island Melee: Flip blocks don't react to attacks
Yoshi's Story: No Randall, no Shy Guys
Peach's Castle: No bumper, sliding platform is static
Balloon Fight: No bumpers/fish/lightning, stalactites are indestructible
Mario Maker: Inconclusive, need more data re: random layouts
Lylat Cruise: No tilting
Gamer: No 5-Volt, need more data re: random layouts
Tortimer Island: No fruit or sharks, layout still random
Kongo Jungle: No barrel, moving platforms are static and roughly level with top platforms
New Donk City Hall: Acts like Prism Tower, not all stops are used each cycle