What is Sandbox mode? plz help and ty

Sandbox mode is a mode which does not exist in the game, but is desired by many. It would let you experiment or practice different things very quickly. For example, if there was a wall you have a hard time flashing over, you could theoretically set the Flash cooldown to 2 Seconds so you could practice flashing over it many times in a very short period of time. If you wanted to see how two items interacted, you could do so in seconds as oppose to waiting a long time in a custom game to get the gold for both items.

Riot made a statement that they weren't going to be making a Sandbox Mode, but went to a "we'll consider it" stance after hearing the community's backlash.

Something Riot has stated they're not looking to ever implement so it's kind of irrelevent

Something some people want but doesn't exist.

Essentially it would just be more options for custom games like starting with a bunch of gold so you can try out stuff without farming for 20 minutes. Some people have mentioned wanting a way to reduce flash CD so they can practice flashing over various walls. Things like that.