This sentence has several examples of affixes:
* un- is a prefix used in "unusual" and "unbelievable" to create the opposite meaning.
* -ly is a suffix used in "usually" and "believably" to create an adverb.
* -s is a suffix used in "dogs" to indicate plural.
* -ed is a suffix used in "showed" to indicate past tense.
* -off is a suffix used in "showed off" to create a compound verb.
Let me know if you'd like to see more examples or have any other questions!