Tetris Ultimate

This achievement requires earning three badges. One is a grind. One is very difficult.

Show-off: Clear 100,000 lines in online mode

This game is long dead, so you'll have to find someone to boost this with. You're looking at about 75-100 hours of online play depending on how fast you can go. Note that your total lines are tracked, but lines earned in online play are not, so be sure to keep track yourself so you know how far along you are.

T-spinner: Complete 3,000 T-spins

If you make it a point to get a t-spin when the chance arises, this should come well before you clear 100k lines for Show-off. Note that you don't need to clear a line for a t-spin to count, but you do need the "t-spin" notification to come up on the screen. Here are some examples.

Simply the Best: Do a 20 combo

This is tough. Really tough. You need to fill the well in a very specific way so that you can drop 21 consecutive pieces and have each one clear a single line. You'll clear 21 lines in this process, with the combo starting on the second cleared line. Here is my run where I fumbled for a while to get things set up properly (which I edited out- boring), then completed the combo. If you want to see the setup, check this video from YT user Jonathan Hart.

After completing the third badge, the achievement should pop. It didn't pop for me initially- it took three weeks until it magically appeared on my profile.

Godspeed.