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Mobile games

You can use an app monetization platform to carry these tasks for you, but from what I understand they require 20%-50% royalty fee
 
Games are very different from apps in general. I'm assuming you're talking about a mobile game.

Highly targeted ads on social media (Facebook, Instagram, YouTube, and Reddit work well in this space), including working directly with influencers for sponsorship spots. Depends on who your target audience is. Hire a social media marketing manager (internal or outsource/agency).

Have a referral program where players can invite friends in exchange for some in-game reward.