My ad is just one image and some clickbaity headline. The image is very simple, high contrast, designed to pop out. I'm targeting all kinds of puzzle subreddits. I'm getting just about $0.15 cost per click in US. The budget is quite small, but this helps reaching out to new audiences who spread the game further to their friends. The majority of the growth is still organic, but ads do help. I'm still not sure if it's a net positive though, since I don't have strong monetization in the game, and don't do any fingerprinting of users, or much analytics at all.