In Tetris 99 you compete against 98 other people with time to kill, trading lines with each other as the crowd is whittled down to 50, then 10, then an eventual winner.
Now, if you've ever played two-player Tetris over the last three decades (with a Gameboy cable if you're nasty), the basic premise is the same. The progress you make (and the lines you demolish) negatively affects your rival, piling on the pressure. With Tetris 99, it's not a two-way process. Here, lines get sent from player to player (you'll see a rough outline of your competitors' boards), shaking things up, regardless of your skill level.
This is done through a secondary layer of controls, beside your block shifting buttons. With the left stick, you can shift your attacks to specific -- but anonymous -- Tetris players. More usefully (and less chaotically), there are four shortcuts accessed through the Switch's right stick. These drive your attacks towards either people attacking you, people close to KO (cheap!) or simply random players. You can also hit 'badges' which represent high-level players with KO badges — if you feel like playing aggressively.
KO badges aren't really explained at all, but the bottom line appears to be: you need to kill players to progress into the final throes of the game. So what do KO badges do in Tetris 99?
Fortunately, players on Reddit have unravelled the mystery. Your badges add an attack bonus to your line number, one badge will give you 25 percent more lines to defend or attack with while a fourth badge will double your line attacks. If you kill someone with a badge, then boom, you get their badges.
What this all means is that even high-level players can feel the heat at any time in the game, if any fraction of the 98-player mass suddenly turns on them. And that's the boiled-down delight of any battle royale game for me: player skill is useful, yes, but so is good timing and luck.