As in English, adjectives come in three forms—positive, comparative and superlative:
Langsom, langsommere, langsomst. (Slow, slower, slowest.)
And likewise, there are a number of exceptions:
Mange, flere, flest. (Many, more, most.)
Adverbs can also be irregular:
Jeg vil gerne, jeg vil hellere, jeg vil helst. (I would like, I would rather, I would preferably.)