gistfile1.cs

public struct MovementData
{
    public float SomethingRelevent;
}

[StructLayout(LayoutKind.Explicit)]
public unsafe struct Movement : IComponentData,IMovementBehavior
{
    public enum MovementType : int
    {
        None = 0,
        Stumbling,
        Running,
        Idle
    }

    [FieldOffset(0)]
    public MovementType Type;

    [FieldOffset(4)]
    public MovementData Data;

    [FieldOffset(4)]
    private StumblingBehavior _stumbling;
    
    [FieldOffset(4)]
    private RunningBehavior _running;
    
    [FieldOffset(4)]
    private IdleBehavior _idle;
    
    public void Move()
    {
        switch (Type)
        {
            case MovementType.None:
                break;
            case MovementType.Stumbling:
                _stumbling.Move();
                break;
            case MovementType.Running:
                _running.Move();
                break;
            case MovementType.Idle:
                _idle.Move();
                break;
            default:
                throw new ArgumentOutOfRangeException();
        }
    }
}

public interface IMovementBehavior
{
    void Move();
}

public struct StumblingBehavior : IMovementBehavior
{
    public MovementData Data;
    public void Move() {}
}

public struct RunningBehavior : IMovementBehavior
{
    public MovementData Data;
    public void Move() {}
}

public struct IdleBehavior : IMovementBehavior
{
    public MovementData Data;
    public void Move() {}
}