As you can see the grass is seamless, and has no sign of a grid, which some think is a very hard thing to do, but there wrong...
1). First step, is make a 64x64 image in any program(This tutorial uses Photoshop). Now, go to Noise, and noise it around 4-9%, whatever fits and looks best to you. Now take that 64x64 and put it into .DM and make sure it breaks up into 4 icons named 1,2,3,and 4. Your done for the first step!
2). Second, now that you have that it already looks pretty good, but it you want a real grass feeling then you have to do this step. First open up .DM and start a new icon, fill in a color as the background. Use 4 colors for this[Step 1](Highlight, Main, Shade, Dark). [Step 2]Fill it with the main and[Step 3] use the highlight color to draw small lines(2-4 pixels tall) upwards, and some to an angle a bit. [Step 4]Use the shade to put under the lines and a lil bit to bottom right of them(If your lightsource is from top left). [Step 5]Put the dark shade in strategic places like in open spaces, or under highlights. Remember for the highlights there is alot of grass blades so have ALOT of highlight lines. [Step 6]Once done with this use the highlight and strategicly place dots in the open spaces, do the same afterwords with the shade, though if you can try to place under the highlights. [Step 7]After all is over add slight dark spots in the grass with the dark shade(Though very small cause they show up).
3). Third, use this new grass image(Try to make it seamless as possible), and change its whole alpha to 30-50%(Choose whatever fits you best). Copy and paste the new image over all 4 icons that were made in step 1. This will give its overall grass effect look(By having vertical highlighted lines). And still be seamless.
4). Now that you have the icon, it's gonna be hard to map, or is it? All you need to do is keep the grass icon_states at 1-4, and use this as your grass icon code...
turf
Grasses
icon='Grass.dmi'
Grass
icon_state="1"
New()
..()
icon_state="[rand(1,4)]"
Thanks for reading and hope you like it! This is my first tutorial so say how it is and what needs to be done, I will shortly make a Cliff tutorial(That I used my style to make the cliffs in NKM(Naruto Kousen Myou), I also used this style for the grass is NKM).