Nintendo Switch Online: 14-Day Free Trial Membership (account set to US) even if you've had a free trial before

Great big thank you to @pirate1 for confirming this works

you can change your existing Nintendo account country at accounts.nintendo.com/profile/edit (have no eShop credit, no active subscriptions, no child accounts in your Family Group [will cost you to re-authenticate them])

• experience online gameplay in Nintendo Switch games which support online play
• play Tetris 99 and F-Zero 99 :- retro style battle royale games
• a selection of NES games, SNES games, Game Boy (including Game Boy Color) games - even online against friends

Method works for existing accounts with saved payment info:
• change account country to US at accounts.nintendo.com
• go to my.nintendo.com and claim your code
• redeem your code at ec.nintendo.com/redeem - select random ZIP Code and your payment method for ongoing subscription
• terminate auto-renewal
• revert your account country

enjoy

Thanks again @pirate1

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all features of Nintendo Switch Online - nintendo.co.uk/Nintendo-Switch-Online/Benefits/Benefits-2060569.html

Online play
Take out rivals and team up with friends online in supported Nintendo Switch titles, such as Mario Kart 8 Deluxe, Animal Crossing: New Horizons and Super Smash Bros. Ultimate.

Tetris 99
99 players…but only one will remain! TETRIS® 99 is the iconic puzzle game as you’ve never seen it before. Can you pick the right strategy to best 98 other players online – all at the same time?!

F-Zero 99
F-ZERO 99 delivers all the action of the original Super NES game, with the added twist of online play. Take on players from around the world and race to be the last machine standing!

Nintendo Entertainment System
Balloon Fight • Baseball • Donkey Kong • Double Dragon • Dr. Mario • Excitebike • Ghosts’n Goblins • Gradius • Ice Climber • Ice Hockey • The Legend of Zelda • Mario Bros. • Pro Wrestling • River City Ransom • Soccer • Super Mario Bros. • Super Mario Bros. 3 • Tecmo Bowl • Tennis • Yoshi • NES Open Tournament Golf • Solomon's Key • Super Dodge Ball • Metroid • Mighty Bomb Jack • TwinBee • ADVENTURES OF LOLO • Ninja Gaiden • Wario's Woods • Zelda II: The Adventure of Link • Blaster Master • Super Mario Bros. 2 • Kirby's Adventure • Kid Icarus • StarTropics • Super Mario Bros.: The Lost Levels • Punch-Out!! Featuring Mr. Dream • Star Soldier • Donkey Kong Jr. • VS. Excitebike • Clu Clu Land • Double Dragon II: The Revenge • Volleyball • City Connection • Wrecking Crew • Donkey Kong 3 • Kung-Fu Heroes • Vice: Project Doom • JOURNEY TO SILIUS • Crystalis • Shadow of the Ninja • Eliminator Boat Duel • Rygar The Immortal • S.C.A.T.: Special Cybernetic Attack Team • Nightshade • Fire 'n Ice • Ninja JaJaMaru-kun • EarthBound Beginnings • Mappy-Land • Dig Dug Ⅱ • Pinball • DAIVA STORY 6 IMPERIAL OF NIRSARTIA • XEVIOUS • Mystery Tower • Downtown Nekketsu March Super-Awesome Field Day! • Joy Mech Fight • DEVIL WORLD • The Mysterious Murasame Castle • R.C. PRO-AM • SNAKE RATTLE N ROLL

Super Nintendo Entertainment System
Super Mario World • Super Mario World 2: Yoshi's Island • Super Mario Kart • The Legend of Zelda: A Link to the Past • Super Metroid • Star Fox • F-ZERO • Stunt Race FX • Pilotwings • Kirby's Dream Land 3 • Kirby's Dream Course • Super Ghouls'n Ghosts • Demon's Crest • Super Soccer • Super Puyo Puyo 2 • Super Tennis • Breath Of Fire • BRAWL BROTHERS • SUPER E.D.F. EARTH DEFENSE FORCE • Joe & Mac 2: Lost in the Tropics • Star Fox 2 • Super Punch-Out!! • Kirby Super Star • Breath of Fire II • Pop'n TwinBee • Smash Tennis • Operation Logic Bomb • Panel de Pon • Wild Guns • Donkey Kong Country • Natsume Championship Wrestling • Super Mario All-Stars • Donkey Kong Country 2: Diddy's Kong-Quest • Mario's Super Picross • The Peace Keepers • Donkey Kong Country 3: Dixie Kong's Double Trouble! • The Ignition Factor • Super Valis IV • Tuff E Nuff • DOOMSDAY WARRIOR • Prehistorik Man • Psycho Dream • Caveman Ninja (also known as Joe & Mac) • Magical Drop2 • Spanky's Quest • Super Baseball Simulator 1.000 • Claymates • JellyBoy • Bombuzal • EarthBound • Earthworm Jim 2• Rival Turf! • Congo's Caper • Kirby's Avalanche • Fighter’s History • SIDE POCKET • Harvest Moon • Kirby's Star Stacker • KILLER INSTINCT • BATTLETOADS IN BATTLEMANIACS

Game Boy (includes Game Boy Color)
Tetris • Super Mario Land 2 - 6 Golden Coins • The Legend of Zelda: Link's Awakening DX • GARGOYLE'S QUEST • Game & Watch Gallery 3 • Alone in the Dark - The New Nightmare • Metroid II - Return of Samus • Wario Land 3 • Kirby's Dream Land • Kirby’s Dream Land 2 • BurgerTime Deluxe • Kirby Tilt 'n’ Tumble • Blaster Master: Enemy Below • The Legend of Zelda: Oracle of Ages • The Legend of Zelda: Oracle of Seasons • Pokémon Trading Card Game • Quest for Camelot • Castlevania Legends • Dr. Mario • Mario Golf • Mario Tennis