plötzlich
suddenly
Describes an event that happens unexpectedly, quickly, and without warning.
Wir saßen im Garten, als es plötzlich anfing zu regnen.
We were sitting in the garden when it suddenly started to rain.

suddenly
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suddenly
Describes an event that happens unexpectedly, quickly, and without warning.
Wir saßen im Garten, als es plötzlich anfing zu regnen.
We were sitting in the garden when it suddenly started to rain.

'Plötzlich' (suddenly) can stand in different positions in the sentence. If it stands at the beginning of the sentence (position 1), the verb follows directly. But it can also stand in the middle of the sentence, usually after the finite verb.
Plötzlich ging das Licht aus.
Suddenly the light went out.
This adverb is an important signal word in storytelling. It marks an unexpected moment and creates suspense or surprise.
Sie las ein Buch, als plötzlich das Telefon klingelte.
She was reading a book when suddenly the phone rang.
'Plötzlich' (suddenly/sudden) can also be used as an adjective before a noun. It then describes a noun that appears or happens unexpectedly and is declined like other adjectives.
Ein plötzlicher Wetterumschwung überraschte die Wanderer.
A sudden change in the weather surprised the hikers.
once / times
'mal' in the fixed expression 'auf einmal' (suddenly / all at once) and 'plötzlich' both describe something happening unexpectedly. 'plötzlich' is a normal adverb and fits in many situations. 'auf einmal' often sounds somewhat more narrative and emphasizes the moment when something changes quickly. It is often used when everything was normal before and then something surprising happens. Important: only the whole expression 'auf einmal' has this meaning, not 'mal' on its own.

Zu Hause ist plötzlich das Internet ausgefallen.
At home, the internet suddenly stopped working.
Auf einmal stand mein Bruder vor der Tür.
All of a sudden, my brother was standing at the door.