pixaPencil ☞ https://f-droid.org/packages/com.therealbluepandabear.pixapencil/

ignore the "source code no longer available". It works fine as it is.

I've been using krita for a while now to do pixel art on android, it works great, but you need to play with the setting to make it work properly.

Recently I found Drawpile, which is based on krita but optimized for android. https://f-droid.org/packages/net.drawpile/