Yes, if followed by a comma.
No, but you can make a sentence with the word suddenly. Suddenly it started to rain.
The adverb "suddenly" typically appears at the beginning, middle, or end of a sentence, depending on the emphasis desired. For example, it can start a sentence for dramatic effect ("Suddenly, the lights went out"), be placed before the verb ("She suddenly realized the truth"), or follow the verb ("He fell suddenly"). Its flexible placement allows it to modify the action effectively.
Suddenly.
Suddenly, The door slamed closed
Suddenly the boy whacked me on the head.
Suddenly, The door slamed closed
suddenly loomed ahead. Predicate is everything except the subject. The subject in this sentence is 'A steep mountain'
Suddenly she lashed out menacingly
Suddenly, we encountered the lunch lady.
Had
I can give you several sentences.Suddenly, the lights flickered and went dark.He suddenly began to cry.We were suddenly surrounded by pygmies.
A man was walking down the road when suddenly his sentence was interrupted by the earthquake.