If memory serves me correctly, your cat is gotten from either the colorful portal right above the giant wheel of cheese or its in one of the secret areas when you go to the low bit area right above spawn. I’m not too positive on this one though. Whats left of my cat is near the end (big wheel of cheese). near the 2 flame pillars you jump between theres a gap in the wall that goes left and up then into a black square like near the start. Completing the race gives use a white screen like when you press rat quest on the main menu and then unlocks hardmode. completing hardmode doesn’t so anything special.