Small scripts and composition

Good gameplay code is built from small parts with one job each: a health component, a mover, a damage dealer, a pickup. Unity attaches components to GameObjects. Godot builds scenes from child nodes.

Unreal adds Actor Components to Actors. Building objects from parts like this is called composition. You can make a new enemy by combining existing pieces, instead of writing a new class or copying code.

It also makes bugs easier to find, because each part is small. Inheritance (one class extending another) still has a place, such as a base enemy class, but keep those family trees shallow.