The movie was about a young girl that found a mirror and there was a passage or another world through the mirror.. In the end she had to destroy the mirror to stop the jagged teeth monster things from escaping... I'm so having a brain fart I uused to watch this when I was younger. That was only like 12 years ago I saw this movie.. I'm 18 now... Please help meeeeeeeeeeee

There are three through-the-mirror films:

The Hugga Bunch (1985 TV movie)
http://www.imdb.com/title/tt0173915/?ref_=nv_sr_1
This has a witch with a special fruit tree under a glass dome.

Magic in the Mirror (1996)
http://www.imdb.com/title/tt0116959/?ref_=fn_al_tt_1

Magic in the Mirror: Fowl Play (1996)
http://www.imdb.com/title/tt0116960/

The latter two have the threat of giant ducks which turn people into tea. In the sequel, they're invading our world.

it wasn't magic in the mirrror. it was a 100% full real world movie.. I'm not sure if it was late 199s or early 2000s... there was a girl about 16 , 17 in the movie. it was a magic movie, but it was deffently not magic in the mirror or hugga bunch.. :(

I know the time frame is wrong, but the general story line (young girl and mirror) is a close match with The Watcher in the Woods (1980)

The Watcher in the Woods (1980) - IMDb

Shot in the dark... maybe Mirrormask?
MirrorMask Trailer - YouTube

Noo not any of those. Hmm I'm really trying to remember the story line I know the costumes were very poor like . Thy were only masks of like "goblins"