The following is an in-depth guide for the mushroom cup of Mario Kart: Super Circuit
This track is very simple with barely any turns at all. If you have a mushroom or a star or anything else that can cut through the offroad you can use it to cut through the corners on a few of the turns. Otherwise, there aren't many things you can do to gain an advantage on this track specifically.
This track doesn't have too many new obstacles to worry about. There are a few sections with some grass on the sides that you have to avoid or it will make you go slower. Otherwise try and stay off of the water. If you have a mushroom, use it on the turn, as this track is basically one big soft square, so if you have a mushroom or star you can use it into the water on the corners of the square. Watch out for the cannon balls shot out of the Shy Guy Pirate Ship. You'll also have to worry about Sidesteppers.
This track doesn't have too many obstacles to worry about, but there is a couple times where you'll go over a bridge and you'll have to be careful not to fall off into the water. There are a couple times where you can cut a corner with a mushroom if you have it, but there's a big mushroom shortcut early on. If you have a mushroom you can use it off the right side into the water just after the first U turn into a board walk and hop over the river to skip a few turns and gain a lead on the competition.
This track doesn't have that complicated of a layout to race on. Near the end of the race there's a spot where you can jump constantly over the bumps in the road. Make sure you're going pretty fast so you can clear every single one. Otherwise there aren't really any shortcuts here. Also make sure to watch out for the lava bubbles popping out of the lava and the thwomps on the road.
Next: Flower Cup