How To Make a "Mappy Railgun" (and Farm Dungeon Guardian) | Terraria 1.4.4

*The floating glitch got patched in 1.4.5, so you can no longer float dummies.
If you want to build it in 1.4.5 or later, please also refer to this video: https://youtu.be/KTkG23p2fVk
1.4.5 Mappy Railgun schematics: https://imgur.com/a/EZ5bEFI

Recorded version: 1.4.4.9

Terrasteel's video
https://youtu.be/jnhtIYht11A

Timestamps
0:00 - Intro
0:18 - Response to Terrasteel
1:21 - How to make the "Sweatproof Mappy Railgun"
6:09 - Dungeon Guardian Farm
7:50 - Outro

I mean, not that I get the term "sweat" gamer kids often use. What's there to sweat anyway? All I do is just sit in my chair and move my fingers lol