Cross promotion is an app marketing strategy in which app developers promote one of their titles on another one of their titles. Cross promoting is especially effective for developers with large portfolios of games as a means to move users across titles and use the opportunity to scale each of their apps. This is most commonly used by hyper-casual publishers who have relatively low retention, and use cross promotion to keep users within their app portfolio.
It’s important not to prioritize cross-promotion ads over 3rd party ad placements, which can actually monetize a game. Rather, cross promotion is a great way to fill unprofitable real estate such as start screens, about pages, game review pages, etc.