I think the more subscribers you have, the more celebration will "work." As it is a celebration, the more the merrier:
Simple celebration ideas:
- Make a simple extra art to celebrate it, then post it.
- You can also make the extra art as a downloadable wallpaper for your readers.
- Make an extra chapter, may it be an additional story, characters biodata, world-building info, or how do you make the series.
- Livestream of your process
Celebration ideas with reader participation:
- Hold a poll
- Make an extra content which requires reader's participation. For example make a poll on which character they would want the extra chapter to be based on.
- Hold a Q&A or AMA for either you or your characters
- Livestream where reader can ask question or what to draw.
For a bigger, more festive celebration which requires reader's participation (recommended for bigger subscriber numbers/engagement), you can:
- Hold a raffle. The prize can be art, ink, or merchandise if you are feeling extra rich
- Hold a contest. The prize can be art, ink, or merchandise if you are feeling extra rich, this also requires more people because you might need a judge panel.
