against a corner, it

[user_gary]

Merlin had an invitation to attend a party one evening. He was a trifle vain and a bit of a show-off as well, who always wanted to stand out, in order to attract attention.
It was a costume party so formal dress wasn't needed. He chose a loud and colourful costume, so that people would notice him, and in order to make a grand entry into the party he strapped a pair of shoes with wheels, to his feet. He made a remarkable entrancy rolling into the ballroom on his skates playing a violin. Eyes popped up in wonder, as people noticed his flashy dress and heard his violin, but what really got them was to see Merlin soar out of control across the hall, as he realized too late that he could not turn or brake. He slammed into a large and costly mirror, standing against a corner, shattering it, smashing his violin, and in the process severely injuring himself.

Please explain the `against a corner', and tell what the `it' refer to?

[engee30]

shattering it (= shattering the mirror)
he shattered the mirror and smashed the violin as well

[engee30]

standing against a corner = a mirror that was standing against (= next to, almost touching) a corner