If außer appears before a noun or pronoun that refers back to another in a previous clauseNo definition set for clauseLorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum., the noun or pronoun following außer can match the case of that previous noun instead of being in dative case — even if dative case is always a correct alternative choice.

Study Resource: Additional uses of the eight common dative prepositions in German
The following are some uses of the German dative prepositions that were not covered in our article.
aus
To express what material an item is made from or of:
Es wurde aus dem besten Holz gemacht.
It was made of the finest wood.
außer(besides)
To express that you are beside yourself with some emotion:
Ich bin außer mir vor Freude.
I am beside myself with joy.
Er ist vor Wut außer sich.
He is beside himself with joy.
In these expressions, the pronoun is a dative reflexive pronounNo definition set for reflexive pronounLorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. not a dative personal pronounNo definition set for personal pronounLorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum., so the third personNo definition set for third personLorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. pronouns aren’t ihm, ihr, or ihnen, but sich.
Tip
bei
To express that locations are near each other:
Das Rathaus ist dort rechts beim Museum.
The city hall is over there on the right side near the museum.
To express that an activity is currently ongoing, or that something is happening while something else is happening or during another event taking place:
Wir sind gerade beim Essen.
We are currently eating.
→ In English, the currently ongoing action is expressed by the ing-form of the verb.Ich will nicht wieder beim Schlafen gestört werden.
I don't want to be disturbed again while asleep.
To express that certain measures will be taken in case of a weather or health condition:
Bei schlechtem Wetter findet das Spiel in der Sporthalle statt.
In case of bad weather, the game will take place inside the gym.
Bei starken Zahnschmerzen sollten Sie schnell einen Zahnarzt aufsuchen.
In case of a bad toothache, you should quickly visit a dentist.
Idiomatic uses:
Er ist nicht ganz bei sich.
He is not all there. (referring to mental state)
mit
To express that someone did something at a certain age:
Mit dreieinhalb Jahren konnte sie schon lesen.
She could already read at three and half years.
von
To express that something by a certain author or artist:
Das Buch ist von Goethe.
This book is by Goethe.
Use von to feel like a duke or duchess — just add it before your last name! Unfortunately, it’s not that easy, but historically, von was used in titles of nobility, so someone with it as part of their last name likely was a member of the peerage:
Alexander von Humboldt war ein berühmter deutscher Wissenschaftler und Entdecker.
Alexander von Humboldt was a famous German scientist and explorer.
zu
Use zu with nouns expressing emotions to say that the emotion occurred due to some event:
Zu meiner großen Überraschung hatte ich einen Preis erhalten.
To my great surprise, I had received a prize.
Zu can indicate that someone lives at a certain place. This is an outdated usage but you can find it in older literary texts, fairy tales, and folk tales:
Graf Rudolf von Hohenfels lebte vor vielen Jahre auf der Burg zu Hohenfels.
Count Rudolf von Hohenfels lived many years ago at the castle at Hohenfels.
Es lebten einmal zu Dresden drei Brüder, die konnten zaubern.
Once upon a time, there lived at Dresden three brothers that could do magic.