Things to know about 2D games!

I am trying to develop a 2D game in Unity…

SO, what are all the things fundamentals and optional
that I need to know for creating the 2D game!!

P.S. I am talking about technical stuffs in Unity and not the creative,artistic Perspective!

P.P.S. I would be glad to know about the extra tools that can aid the 2d Development!

If you mean 2D as in “the player is restricted to movement in only two dimensions”, then:

If you mean 2D as in “graphics will be created as sprites rather than 3d models”, then: