Archetypes are recognizable characteristics that we use to categorize people or things into groups.
For example: A woman who is a perfect mother and wife, a giving member of her community, and a societal model of morality might be archetyped in a book as "an angel," or even as "Eve."
Theses are the type of characteristics that create a motif in the reader's mind of good, bad, silly, morally corrupt, etc...
Allusions are leading to a conclusion without absolute description. An author may alude to the fact that a character is doing bad things without showing the action of a bad deed. Allusions are a more ambiguous way of leading to the building of archetypes, while archetypes are often more recognizable which enables grouping into absolute patterns.