Use the round or square pixel brush. This includes erasers!
here are my settings for both tools.


Feel free to adjust smoothing, I usually use 80%
the airbrush can stay unchanged for a better gradient effect.
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Fillings have different opacity based on thickness.
soda = 50 - 75%
tea = 95%
Ice cream or milk = 100%
boba's will sink into thicker fillings, so you're welcome to cut pieces off, or use the fuzzy eraser to make them fade.

soda can have a neat fizzy effect too! It's kind of tedious to make, but it looks really cute.
To make the babu's fizz, we would build custom sparkles all over the body using white single-pixel cubes. Always use singular pixels and build up to star shapes or orbs. Like snowflakes, but made out of the tiniest of pixels.
for an added shimmer, try playing with the sparkle's opacity. A favorite of mine was to duplicate the layer, move it around a little, and then turn it into an overlay!
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Boba's can be the trickiest part if you're not sure what to do with them.
they can go anywhere in the bab's body in any amount!
These basic boba are made of two circles, both at 100% opacity. Usually under the shell layer.
Large circle = 22 pixels
small circle = 12 pixels

smaller bobas can be sized around 15 for the larger circle and 7 for the smaller one
Popping boba is a favorite of mine, but a little different.
using the same 22-pixel brush, make two 22 sized circles. Each on their own layer but overlapping.
Next, make the bottom circle's opacity around 50%, or whatever looks good with your colors.
Then, using a size 18 eraser tool, cut a hole in the center of the top circle.
Then just add some shines!

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hair is a lot more free form.
you can do it lined or lineless, with as much or as little detail as you want.
the basic idea is to start at the base of the ears and work your way around the head.
starting with bangs and then going down along the neck for longer styles.
Lineless, you can start by just gesturing out strands of hair into a shape and then filling it in by hand.
Lined you can sketch out the outline of the style then use the fill bucket to fill it.
(note, fill bucket requires every single pixel be closed. So if you have even one tiny pixel out of place, it won't fill correctly)
adding colored strands is a great way to get more detail!

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That's all the biggest details I could think of!
If you guys have more questions or techniques you'd like me to show, feel free to comment and I can add more! <3