Build the game projects — mechanics, feel, and a build that actually ships to a store.
Games are one of the things we sell, and they are the least forgiving work we do: if it does not feel right, nothing else about it matters.
You will work on mobile-first titles where frame budget and install size are hard constraints. Prototyping quickly matters, and so does knowing when to throw a prototype away.
Send a build we can play, even a small one.
Unity and C#, mobile performance profiling, some 2D or 3D maths. Published work counts far more than a showreel.