Tetris 99 is a neat example of how the design can result in unintuitive optimal strategies at high level play.

Two mechanics that come to mind are (1) targeting bonus and (2) the finite garbage cap.

1. Targeting bonus makes it so that if multiple players are attacking you, your attack is buffed. Intuitively it makes sense, since it evens the scales a bit: If, by happenstance, you are unluckily targeted by multiple people, at least you have a fighting chance at surviving the 1v2 or 1v3 etc.

One counterintuitive consequence of this, however, is that an optimal strategy to farm KOs is to stack very high on the board so that you are in danger of topping out. A reasonable number of other players will have their targeting strategy set to KOs (since it is 1 of 4 options), and will target you. If a massive number of players are targeting you, a reasonably skilled player is in no danger because they can easily offset incoming damage with singles or doubles, buffed by targeting bonus.

Example of a game using this strategy to achieve 51 KOs: https://www.youtube.com/watch?v=cat9TbAwRWU

Another consequence of this is in the teams mode, if the teams are imbalanced, counterintuitively, a top level player would prefer being on the smaller team over the larger team. To be fair, there is a certain skill floor required to survive the initial onslaught. But if you can survive and get KOs, the attack % buff you get from the KO badges will eventually give you an advantage over the larger team, eventually to the point where victory is almost guaranteed.

Extreme example of a player winning a 1v98: https://www.youtube.com/watch?v=OTE4zEKtxkA Most normal players would not survive the initial influx of garbage. In particular, because the garbage meter is constantly full at 12, you are not even outputting any damage at all unless an individual line clear sends 13 or more (in which case, 12 of that cancels the incoming garbage, and a mere 1 attack is sent out).

But once you start getting KOs, you start getting badges, and eventually by the time the opponent team dwindles enough that you no longer have targeting bonus, you will have a +100% attack bonus from full badges, and you should be able to easily destroy the remaining players.

2. There is a garbage cap of 12. Which means if your garbage meter is full and more attack comes in, it just vanishes.

Intuitively this makes sense for balance reasons, to make the game feel less RNG/frustrating. If you are unlucky and receive damage spikes from multiple players simultaneously, your incoming garbage is never more than 12, so at least you have a reasonable shot at surviving.

A consequence of this however, is if you are on the backfoot and your garbage meter is filling up, it can be better to play slow than to play fast.

For example, suppose you have 8 incoming garbage. Instead of playing quickly, it can be a better strategy is to not place the piece, and wait for your opponent to send. Suppose your opponent sends 10 attack. Here, only 4 of that will go into your meter, and the rest will vanish. Then you can accept the garbage, and you will be in a better position than if you had played fast.

Even if you are at a badge disadvantage, it's possible to catch your opponent off guard with an unexpected counterspike, expecially if they have just sent everything and have no resources to defend.

Example of a Tetris 99 game where the final 2 lasted for 23 minutes: https://www.youtube.com/watch?v=DoLh5w5rwS0 At 19:55 you can see Amemiya stalling until he sees that Doremy has no resources on his board, and then counterattacks fast.

A few years back, HardDrop hosted Tetris 99 snipe lobbies, and those lobbies would stretch excruciatingly long because even with badge disadvantage, reasonably skilled players are very, very good at stalling.