Turnip Boy Commits Tax Evasion

Update! Graffiti Games posted the following on July 15, 2022:
Huzzah!

Note that several people have reported having to uninstall/reinstall the game or hard reboot in order for the achievements to unlock. Personally I was able to clear this one no problem but until I did a hard reset, I couldn't walk back to the greenhouse without the game crashing for the Nuke achievement.

Once you have beaten the game, the Limitless Line (endless train) opens up across from the sub shop in Layer Lane. This is an endless roguelike mode moving from train car to car fighting enemies and bosses. About 8 rooms in is a boss fight with Conductor Onion, which you have to beat once for another achievement.

Once you've defeated Conductor Onion once, and revisit the train, there's a chance for ??? to spawn in a room on the train. It's a relatively small chance, so you'll probably have to visit the train several times to get it to appear. Once you have defeated ??? the achievement will unlock.

Some have reported meeting ??? before Conductor Onion, so it appears that is possible as well.

I went through 5 loops before ??? appeared. I played with 3x damage and God mode on.

??? Is on the endless train that appears after beating the game.
Check your mailbox for a ticket that lets you ride.

Here is my achievement guide, for every single achievement in Turnip Boy Commits Tax Evasion.

For this achievement, you will need to beat the game to gain access to the train (found in the western part of the map, initially blocked before beating the game).

Board the train, and fight through waves on enemies. You will need to beat a few waves to come to a boss fight. Beat all the bosses from the game, and then you will fight the conductor. After this, I got myself killed, and restarted. After about a little over 3 rounds of all the waves (including the conductor) I got the "???" enemy. Super easy fight. If you're struggling, turn on god mode and x3 damage dealing in the settings.

There are guides here showing how to unlock this achievement, so mine is just a heads-up:

The ??? and Destroyer of the World achievements are FINALLY fixed and can be unlocked after completing their requirements.

In order to have access to the Sunset Station, you've got to beat the game once.

The ??? is unlocked in the Sunset Station, where you get in the train and face waves of enemies. After clearing some waves, you will face the Conductor. You can easily beat everything there with God Mod and 3x Damage.
I managed to face ??? after beating the Conductor 4 times. In my 5th run in the train, ??? spawned. Once you beat ???, the achievement pops.