Wait... whaaa??
1. Center 4-wide combos: While largely hated, this is not a "luck based" strategy. Its memorization of the various forms that a center-4wide well creates, to maximize the quadratic damage formula of modern SRS Tetris Games with respect to combos. Perform the longest combo, you deal a LOT of damage.
2. Perfect clear players: I've played vs people who can consistently get 2-perfect clears at the beginning, and often times can hit me with a 3rd. Perfect-clears do 10-rows of damage (against a typical Tetris field of 22 or so), so 2x Perfect clears in the opening is darn near lethal. Regardless, the "Perfect Clear" is the epitome of "planning ahead".
3. DT Cannon: Amemitaya loves his TSpin Double + TSpin Triple setup, and can even perfect-clear or side-4wide afterwards.
4. TKI: A technique to get a TSpin-double within 7-drops. Its the fastest way to damage the opponent, and can stuff a Perfect-clear opening (it takes 10-drops to create a perfect clear. It only takes 7-drops to TKI).
5. BT-Cannon: The reversed DT-Cannon is a TSpin Triple followed up by a TSpin Double. It has different properties and its own set of followers. Honestly, I don't understand this at all, but that's the cool part of SRS Tetris: there's lots of different strategies!
Some Youtube References for non-Tetris folk:
1: Wumbo does 4wide when he gets serious: https://www.youtube.com/watch?v=ieLTP0mIV0o
2. Wumbo also does Perfect Clears sometimes: https://www.youtube.com/watch?v=1YjTu0mByfg
3. Amemitaya usually does DT Cannon into various followups. I can't find any Amemitaya videos, but this guy on gets the concept: https://www.youtube.com/watch?v=bJVN0Wlv-Uo
4. TKI followed up by King Crimson: https://www.youtube.com/watch?v=UXraaMWK6PI . You can see the speed at which TKI is executed, which makes it good vs Perfect Clear players.
5. BT-Cannon->CSpin Perfect Clear loop: https://www.youtube.com/watch?v=umNTGq9p0qQ
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There are a LOT of different strategies in modern "fast" Tetris games. You play vs the same opponent a lot, like first-to-20 or so, to figure out which openings they like and try to switch your openings to best theirs.
Anyway, the main difference between "Modern Tetris" and "Classic Tetris" is that the RNG of modern Tetris is far more forgiving. "Classic Tetris" is a truly random piece, with a lookahead of 1.
"Modern SRS Tetris" is a bag-RNG (every 7-pieces are permuted, and then given to you in a random order), ensuring an even distribution of pieces. Furthermore, you have a lookahead of 5, so you can plan out your strategies far more reliably in Modern Tetris.
I personally prefer SRS Tetris. But I give credit to the classic-Tetris players. Due to the RNG being so much less forgiving in classic-Tetris, its an entirely different skillset and a different game. Furthermore, SRS Tetris is more forgiving with placement of pieces. SRS Tetris looks faster: but a lot of it is because its controls are easier.
Classic Tetris is kinda like watching a Street Fighter 2 player. Laypeople won't be able to tell how difficult some of those moves are. SRS Tetris is more like Dragonball FighterZ, with easier to do combos and automatic-tracking enabled. The combos are flashier and longer, but that's because they're way easier to do than SF2 combos.