4-Wide (4列REN)

If you get 4 wided you're screwed
GOtta 4 wide back
Unless you're just way faster and better than them 🤔

OnePunMan

In modern guideline Tetris, IMO if you don't know how to 4w or haven't bothered learning it, then that's your problem.

Captivate

Knowing 4 wide is good
Knowing nothing but 4 wide is bad

OnePunMan

4-Wide, fourwide, or 4w, is a stacking method where you leave 4 columns open with 3 residual blocks (marked sky-blue above) on those columns. If you stack this way, clearing one line with a mino will again leave 3 residual blocks. Your primary goal is to chain these line clears to do a high number of combos.

Attacking this way is so efficient that 4-Wide became infamous for being broken. In current guideline Tetris clients, starting from combo 9, each single line clear sends 4 lines and more on later combos. This is 2 times more efficient than a T-Spin Double, which sends 4 lines with a double line clear, and 4 times more efficient than a Tetris, which sends the same amount of garbage while clearing 4 times the number of lines. 12 to 13 combos is almost always enough to beat any opponent.

One of the very few downsides of 4-Wide is that misdrops are usually fatal.

Center 4-Wide

Having the 4 columns open on the center is relatively harder to build than just having open columns on the side, but it helps you avoid being topped out by spikes. Since the game has an invisible buffer above the playfield, you also preserve your stack. This means that you can accept a large amount of garbage while also retaining your combo potential.

It is extremely hard to beat an opponent using Center 4-Wide when you have equal stacking speed as your opponent in official clients.

Opening Bag

On stacking your opening bag when you have a SZ and TS/TZ start, respectively. The right side is built like the third picture.

Subsequent Bags

The easy way is to repeat LOJ on one side and to repeat ISZT on the other.

Doing this won't be possible for every sequence, so you'll need to learn some other ways to stack these sides. Go to Tetris.wiki's 4-Wide construction patterns to see some alternate patterns you can use. Practicing sprints with 6-3 stacking is a good way to learn these patterns naturally.

Generally, creating these kinds of surfaces give you a higher chance of continuing your 4-Wide stacking:

Creating a flat surface and doing this isn't good.

thanks to mat1jaczyyy for the tip on surfaces

Side 4-Wide

Can be used as a way to play against Center 4-Wide, but it won't beat Center 4-Wide. Stacking Side 4-Wide can be easier than stacking Center 4-Wide, but unlike Center 4-Wide, you are susceptible to being spiked.

Opening

Just put an I over there and start stacking up. Using a T or a Z are other options.

Building Side 4-Wide is also possible after certain openers. Using it as a follow-up after an opening DT Cannon would be a popular example.

Mid-Game

Side 4-Wide can also be used as a mid-game technique. This is not as good as an opening 4-Wide as you can only do a limited number of combos and also due to the fact that you are susceptible to being spiked while building it. Therefore mid-game Side 4-Wides are generally accepted as a legitimate strategy.

People usually spot these residuals mid-game and stack up on the side.

Residuals

This video will give you a general idea on how to continue your combo. Harddrop Wiki has a nice table on its Combo Setups page.

Other Residuals

We defined 4-Wide as a stacking method where you leave 4 columns open with 3 residual blocks, but it can actually have a different number of residual blocks. 3-residual is just the easiest to set up and maintain.

Some notable ones are 6-residual, which has the greatest combo potential, and 4-residual, which can be done without any soft drops 99% of the time. 4-residual is much more challenging to maintain, and it is therefore mainly used by bots.

Resources

4-Wide Trainer by DDRKirby: A super nice resource for practicing 4-Wide combos. Shows you placement suggestions on the left and lets you know when you make a placement that will eventually end the combo.
Tetra Legends's Combo Challenge would also be a convenient way to practice 4-Wide with 3 residuals.
NullpoMino also has a combo mode called Combo Race, but you'd have to download and install the client in addition to installing Java.

FOUR