Should you happen upon a tyre iron behind the door to Greenhouse Five, put it right back. It's there to keep the enchanted toadstools from overgrowing the entrance.

Oh--and the purple spots can be got rid of with an application of murtlap essence.

(In my day, the compost heap could always be counted on for a good supply of dungbombs. There's nothing like setting one off in front of the Slytherin common room entrance, especially when it's laced with the leaves of a mimbulus mimbletonia: takes days to get the stink out. But I know no one does that anymore; too outdated.)