Here's the Mushroom Cup in 150cc. Normally seen as the easiest cup. Be sure to watch out for Mushroom Gorge though, it's a killer when trying to go for a high rank.
Tracks:
Luigi Circuit Moo Moo Meadows (reappears in Mario Kart 8) Mushroom Gorge (reappears in Mario Kart 7) Toad's Factory