The feature add-to-app is one of the most important when we are faced with the need to migrate an existing Native app to Flutter. It provides ways to modular inclusion of specific functionalities or components made on Flutter within an native application. Avoiding the creation of a ""Perfect Monster"" in this context refers to the potential pitfalls of overcomplicating the codebase or facing unforeseen challenges when combining Flutter with native features. This talk first explores the fundamentals of feature add-to-app, emphasizing their role in promoting a modular and scalable codebase. Then I'll show insights into best strategies for developers to sidestep these challenges, emphasizing the importance of thoughtful planning, clear architecture, and regular testing etc. I have been working in big tech commpany for the last 4 years as Mercado Bitcoin, Nubank, and now Serasa experian, and I've always come across these migration challenges. The most problems I got migrating apps with Flutter some of them for today Flutter has quick ways to resolve, the others I had to get it in the skin to learn void them now.