Welcome! I will just explain a few things that I saw.
The movement controls in your group do not do much, the condition should be 'key is down' rather than 'on key pressed' which is a trigger one event. The platform behaviour has something called 'default controls' which is where the arrow keys work for moving. Because this is enabled it is actually this which is working for the movement and not your events, which is why disabling them has no effect. If you untick 'default controls' on the platform behaviour you can start to simulate your own controls.
Slash is created at its size in the editor around 24x24 whereas the player object has been adjusted in the layout to be a bit larger so this is why the player is larger than the slash object. You need to adjust its size in the editor or when the object is created. Also you are trying to set an animation from another object, you cannot do this and the animation must be on the slash object.