Your graphics overall are quite impressive. You should consider donating more graphics/tilesets/sprites templates to SGDK2, or maybe even doing the artwork for the program, as BlueMonk recently mentioned the incomplete about dialog. I'll comment on your tutorial as soon as I'm done reading it.
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Okay, done reading it. There are some grammatical errors, and sometimes you sound a bit like Yoda, but everything was completely understandable, and the pictures were surprisingly easy to understand, considering the number of arrows and shaded bits. I noticed you didn't include single or double internal corner pieces. It could be a helpful addition later on, but for now, it certainly is a good tutorial.