Pixel art is whatever you make it out to be. We just have our own rules for submission.

But generally yes, pencil tool only. And how else are you supposed to get dithering if not by a pencil tool? Filters? O_O

Okay, so it's basically the AA on the 1 pixel brush that is frowned upon.

This is such bs. I wish people would stop spreading this around (not targeting you specifically, gr, you just happened to be the one who said it in this instance).

Pixel art is about control and precision. Any tool which takes control away from you and puts it in the hands of the computer is frowned upon. A tool that does so and is also well beyond your capability to reproduce its effects is much worse.

Now, there are tools and techniques which seem to take control away from you, but they don't really. Take the fillbucket. It makes the computer automatically fill in a large area with color out of my control, so it's not pixel art right? Wrong. It's a time saving measure. A monkey could fill in that same area. Doing it by hand is a pointless and tedious waste of time.

Also take a rough early sketch. Even if done with only unantialiased brushes, the result can't really be called pixel art, but that's how a lot of artists begin their pixel art pieces. They continuously refine, using finer and finer pixel art techniques, until the end result is, no one doubts, pixel art.

Any tool which adds a million colors to your palette takes control away from you and is frowned upon. The control inherent to pixel art extends to the palette. A thoughtfully managed and controlled palette is, to me, just as much a thing of beauty as the art itself. If your opacity effects do unexpected things to your palette, consider doing them by hand.

Anyhoo, this is all obviously just my opinion. Gallery pieces are taken on a case by case basis. The most important thing is to be absolutely upfront and honest about your methods. If you use a trick that you're unsure about, say so in the description of the gallery piece. It may or may not get in, but your honesty will be admired and your credibility will be augmented. The next logical step is world domination.