Final fantasy 1-9 are on the App Store. Maybe a game that wasn’t originally in a mobile gimmick format could kill some time for you. 3, 5, 6, 7, and 9 are all very good (you don’t need to play them in any particular order. These are all more classic turn based JRPGs. There is also final fantasy tactics which is more of a grid based combat system similar to fire emblem or chess. All the stories are good and engaging

Pretty sure your username is how you kill 20 hours.

Don't kill your time. When you're in the final moments of your life you'll most likely wish you had more, so make the effort to be thankful for every second you have now.

Depending on the airport/country you are stuck in, you can take a trip to the nearby city. I was once stuck in Singapore Airport for 13 hours and just took a day trip to Singapore. It's a bit risky in your scenario because they might move your flight forward but depending on the circumstances of the delay it might be fine.

Almost all airports have a spa or some kind of wellness offers. Would be a great time to try it out. Maybe you discover something new you like, worst case scenario you wasted 1-2 hours. In general look up entertainment offers at the airport. Most have at least an internet cafe that would allow you to play "proper" games since mobile games aren't yours.

If you enjoy adrenaline & frustration, Super Hexagon is one of those thumb-twitchy games that gives you the "just one more" impulse when you die. Unpossible is another.

Do lots of drugs

Baba is You. It is one of the best puzzle games ever made, and available on mobile.

Talk to people? Does the airplane have a bar? Even if you don't drink there's probably people there willing to have some conversations.

I’ve bookmarked all the game suggestions in this thread myself, but haven’t tried any of them yet other than Sudoku. I have the Sudoku.com app.

Badland is a good time-killing game. Having headphones and playing with sound adds to the experience. Not sure if I paid for that one or not.

Minesweeper is a classic one that I don’t think requires internet connection.

Slither.io requires internet but is also a decent time killer.

Airline Commander is one that I’ve downloaded but haven’t tried yet. Airplane simulator that looks interesting.

This is just going through my Games folder on my Home Screen and thinking of which ones I’d play in your situation.

Ketamine

Airports are near cities. Go do tourist things in the city.

Last time I was stuck, I downloaded the Lemuroid emulator and went on to explore retro games. Phantasy Star IV was quite rad.

This is the perfect moment to write a short story

Download a textbook on a topic you're interested in and read it, see how much you can learn by the time you land

Put an alarm and sleep.

Is starting a conversation with someone an option?

Read Das Kapital Volume I by Karl Marx

Brotato, if you are using an android device.

https://play.google.com/store/apps/details?id=com.brotato.shooting.survivors.action.roguelike

If you could get a rubix cube or something at the airport, (which seems plausible) could be a lot of time spent on learning how to do it if you download instructions beforehand.

Learn Chess!

Lifelong pain at a mediocre level guaranteed!

Super neat game though.

I probably sound very traditional but… talk to someone? Make some friends? Call someone?

Buy a fat book.

Read webtoons!

If you truly didn’t enjoy Stardew Valley, then never mind ignore this. If you felt like it had potential but it just didn’t grab you, I’d suggest giving it another shot. It hooks some people immediately but it is a bit of a slow burn for others. It’s beloved by its cult following for a reason. But again, if you didn’t like it then that’s totally legit.

If you like puzzle games, The Witness is another exceptional PC game that was impressively preserved in its entirety when it came out on mobile. The visuals are stunning (though you may not get the absolute best experience on a small phone screen, but still) and it’s got a well-earned reputation for being one of those fully-suck-you-in-lose-track-of-all-sense-of-time games.

Fuck, I could use 20 hours where there's nothing that could guilt me into feeling I could be spending my time better than gaming. Go find a nice comfy couch somewhere and just veg man, enjoy your freedom from responsibility for 20 hours. Won't happen often.

In case you get stuck again and need more games:

• DevilutionX (free, open source, needs gamedata) lets you play Diablo1 on Android, very good time killer (you might need to fetch the gamedata somewhere)
• Out There: Omega (paid but one time purchase) is a relaxed starship roguelite
• Battle For Wesnoth (free, open source) fantasy style tactical game
• Jagged Alliance 2 Stracciatella (free, open source, needs gamedata) - Jagged Alliance 2 on Android, tactical RPG, great timekiller like classic UFO or the old Fallout games.

Notable mentions: WorldOfGoo, Human Resource Machine

You appear to still have about 6 hours left, so go mess around on the travelators, those are always fun.

Learn chess