Turnip Boy Commits Tax Evasion

Upon completion of the main story, when you return to the game there will be a ticket waiting in the mailbox for the limitless train.
The train is located to the left of the starting area and then through the path to the right, across from the sub shop.
You enter the train by the conducter. On the train you defeat waves of enemies and end up fighting each of the bosses from the story. The last boss for your first run through will be the conductor.
If you struggle with the combat or just want to rush you can turn on damage multipliers and god mode through the options.

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. Super easy fight. Dodge the thrown shurikens and kill him. If you're struggling, turn on god mode and x3 damage dealing in the settings.