NPCs in Æther can be created one of two ways. You can choose to create them as a standard character, giving the character points in attributes, then skill points then bonus points. Advancing the character is as simple as giving more skill points and spending them accordingly. That process can keep the bad guys the most fair, and the most in line with the characters.
Sometimes you might be in a hurry though, and you might just want to give the bad guys some stats; and you don’t have an archetype available that fits the bill. Assigning stats on the fly can work, but it takes some practice to get the mix right. Too many attribute points or skill points and the challenge is too great for the party, too few, and it’s too easy. Experienced Narrators know what their parties can and cannot handle, and the enemies and NPCs need to be tailored to the party as well as the adventure.
The purpose of the NPC is almost as important as the attributes and skill values. If the NPC is to be in for the long haul, then the character needs to advance along with the PCs. If the NPC is a short term opponent or ally, the skills and abilities that the character has can be far in excess of those of the PCs. If the PCs are too over shadowed though, they may not have fun because they feel powerless against them or useless beside them.
The same can be said for any system, but in Æther, little tweaks to skills start making a huge difference in a hurry. Twenty points there, or a Base Attribute Modifier of another 10 is a gigantic advantage in most cases.
Keep things going with the NPCs, they are an integral part of the adventure, and should not, in most cases be considered part of the furniture of the setting. Not every NPC needs a name, but the important ones do, and they need attributes and skills to make the encounters memorable, especially if the plan is to keep them around for a while.