Hi! Regarding VFX issues - this is a well known Godot issue and it occurs because materials and particle shaders has to be compiled for a specific device once they first appear in a scene. The solution is simple - create a scene that will show up on game start and under the overlay spawn every material (can apply to a cube for example) and particle system for a few frames, this way the shader compilation will happen before the game start and there will be no lags during the gameplay.