Has anyone who is not in Slytherin been able to get in the Slytherin commone room. If so how did 你 do it?

你 have to make the Polyjuice potion.

你 used to have to brew the Polyjuice Potion first.
Now, all 你 have to do is go to the right moment and zoom in. 你 pass through the 墙 and are in their common room.