Hitboxes, they are simple, but they make or break a lot of the feel with certain moves. Though we can't see them, we can definitely know the kinds of effects they have on the gameplay. These tend to get glossed over in a lot of MUGEN characters simply because "If they can't be seen, why put thought into them?" Well, they are very important, and it's crucial to know how to make them work properly.
Elecbyte tried explaining how to do hitboxes in their own guide, but it was mostly misinformative. It provided good points, but there were blanket statements ("You should always do them like this") and some things that were just incorrect ("Never add disjoint"). There is also no absolutely correct way to create hitboxes. They vary depending on the style of character you are creating. Here are some terms and techniques that are frequently used in hitboxes that you can use.
Hitboxes require some sort of structure. I like to call it the Skeleton. It is basically how you go about making the hitboxes in regards to the motion of the character. Of course, each character looks different, so the same sort of strategy can't apply fully to all of them. First, lets look at idle animations.
Structuring with various idles and 2/3 hurtboxes
When it comes to structuring, a prevailing question is how many hitboxes should you use on a character? Well, it is a preference. Usually it is a range of two to four. What I would suggest is to keep it consistent. If you prefer to use two hitboxes, try to keep it only two hitboxes. If you use three hitboxes, keep it at three, and so on. It just makes it easier to view and to do on an individual level.
With simple idle animations like these, it is best to divide the boxes up. If you're using two hurtboxes, you allocate one box to the upper body/head, and the other to the lower body and legs. If you use three hurtboxes, you divide them up into head, body, and legs. If you use four hurtboxes, you divide it into head, upper body, lower body, and legs. You can simplify some animations as well, for example many idles that have three hurtboxes can use two and be just fine otherwise, but if you are not sure it is best to keep the same number of boxes for consistency purposes. Here is the same idle animation (CvS2 Ryu) but with two, three, and four hurtboxes respectively.
Structuring with CvS2 Ryu's idle and using two, three, and four hurtboxes respectively.
As you can see, it is easy to apply a certain hitboxing style onto any character. It simply comes down to execution. Here, you can see the division mentioned earlier in practice.