Welcome to my guide on how to get the Mostly Harmless achievement.
Before we start there are some you may want to know:

-As of right now I know two ways to pull this off and I will cover both ways in this guide.
-You do not have to worry about your health when doing this since a Green Slime does 100 damage.
-Seeds may or may not work in the future of the game! The developers might change it to now work in seeded runs.
-Seeds will change if the game gets updated so the using old seeds may have different effects then you might expect (I will be updating the seeds on this guide!)

For some community stuff:

-Feel free to contribute seeds and good quality videos as either guides or walkthroughs they will be highly appreciated! =D
-Any info tips or tricks are also greatly appreciated!
-Everyone is amazing <3

Introduction
Contents
Dove method: Step by step guide
Cadence Co-op method: Step by Step guide
Seeds

Many big thanks to cyberdelika for this higher quality video then I had on how to do this!

1. Go to the Character Select and select Dove.

2. If you wanna do this in "zone 1 mode" you have to have unlocked the Black Scroll in the shops. Otherwise you'll have to do it in "All Zones Mode" (There are seeds down below for Seeded Runs)

3. Keep resetting your game until you find a shop with a Black scroll. It should range from 1-7 gold in price so it's easy to get once you find it.


4. Once you've found a Black Scroll go find yourself a room with a Green Slime in it. Try to find a room with the lowest amount of enemies but with a Green Slime. Blue Slimes shouldn't be a bother since they always stay in the same place. But Bats or Skeletons might pose a threat.

5. No position dove next to a Green Slime. She can be above, under, the left and on the right side of the Slime.






6. Now BEFORE you use the Black Scroll, confuse the enemy by attacking it.

7. Once the enemy is confused you can use the Black Scroll and the enemy will jump right into your guts.

More thanks to cyberdelika for another video ^_^

So if you are unsure as to how I did it in the video above, here is a walkthrough.

1. First go into the options menu and bind your keys properly. You can bind the movement of the second player to the numpad keys if you are using a keyboard.

If you are using a gamepad you can configure it to your other analog stick or your buttons.

You can configure them how ever you prefer, these are just examples.


2. Activate Co-op in the main Lobby.


3. If you wanna do this in "zone 1 mode" you have to have unlocked the Black Scroll in the shops. Otherwise you'll have to do it in "All Zones Mode" (There are seeds down below for Seeded Runs)

4. Keep resetting your game until you find a shop with a Black scroll. It should range from 1-7 gold in price so it's easy to get once you find it.


5. Once you've found a Black Scroll go find yourself a room with a Green Slime in it and clear it from other enemies.


6. Now position your characters in a in such a way that the character with the black scroll will be on one side of the green slime and the other character on the opposite side. Much like this:







The Cadence on the left has the Black Scroll.


7. If the black scroll is activated right now the Green Slime will run into Cadence and kill her.

These seeds have been found by the community <3
I do want to remind you that outdated seeds won't work on newer versions of the game and that the developers can remove the ability to get this achievement in seeded mode at all!
You can contribute new ones at all times <3


Game [Version 1.0.0] Up until [Pre-Amplified] compatible seeds:

Seeds:
2074891 by cyberdelika
Go to the bottom left from start and follow the corridor into the room. This room has a Green Slime and an access way into the shop where you'll find a Black Scroll.


3727060 by Flypunk
Go to the top right and follow the corridor into the room. This room has a Green Slime and an entrance to the shop with a Black Scroll on the right side.


2603466 by dukelover
There is a black scroll in the shop to your left. A green slime is located to the right and then down from your spawn.


Game [With Amplified] Up until [Version 3.0.0] compatible seeds:

16634441 by Shenkenstein
To the left is the shop with the scroll and to the right is a room with a green slime.

1125924 by Lomanic
"For Dove with the current version of the game. The green slime is in the room below and the shop is to the left of that." -Lomanic

3727060 by s0r
"If you didn't unlock Dove yet and only have Cadence to work with, because it has 2 slimes and a very handy "arrow-trap" if you pick co-op and then make use of the arrow, when using the scroll from the shop. It will be an easy achievement to get. If you position the players right the slime will run into them." -s0r