It's actually very simple.
Code:
AddEffect = Attachable
PresetName = Coattail
Mass = 2
Sharpness = 0.1
HitsMOs = 0
GetsHitByMOs = 1
SpriteFile = ContentFile
FilePath = *YourMod*.rte/*TheIsolatedCoatSprite*.bmp
FrameCount = 1
SpriteOffset = Vector
X = -*Half of the width of the sprite (In Pixels)*
Y = -*Half of the height of the sprite (In Pixels)*
AngularVel = 60
AtomGroup = AtomGroup
AutoGenerate = 1
Material = Material
CopyOf = Grass
Resolution = 4
Depth = 0
DeepCheck = 1
JointStrength = 5000
JointStiffness = 0.6
JointOffset = Vector
X = 0
Y = 0
Joint offset is where on the coattail it connects to the actor.
Then, inside the actual actor part of the code, put:
Code:
AddAttachable = Attachable
CopyOf = Coattail
ParentOffset = Vector
X = 2
Y = 7
This is where on the actor the coattail appears.
That basically makes the it appear on the actor 2 pixels to the left
(when the actor is facing right), and 7 pixels down.
Replace all the things in the asterisks (Leave the "-" on the sprite offset part).
Also, copy/pasting it will work fine. But you have to change the stuff in the asterisks.