Multiplayer Initialization
In order to get both players initialized. I used Unity's Player Input Manager component to spawn prefabs that have each have a custom PlayerConfig class that holds the PlayerInput component, the ScriptableObject of the selected character, and the player index. I use a custom ConfigManager class set to DontDestroyOnLoad to store the configs. When the game starts, it spawns each players character prefab it its set location and initializes the different components on the prefab that need a reference to variables in the config class or to subscribe to the controls' events on the PlayerInput component.
Grab Mechanic
I was responsible for implemented a grab mechanic on top of our existing move system. Our system gives each move its own flag and has fields to use hitboxes and hurtboxes. I added a grab input in the input actinos and assign players a grab hitbox, setting it up so it's behavior was in line with the game's game design document.
Main Menu & Character Select
For the main menu and character select, I tried using an additive scene loading approach. Since the main menu and character select share the same backdrop, and that back drop needs to listen for an event run on the character select to start animating, I have the backdrop in its own scene that persists when going from main menu to character select or vice versa. I also set up a system in which the players can see whether they're player 1 or 2 and the respective controller type they're using, using this information to initialize the character select as well