The noun allusion means an indirect mention or passing reference to a person, event, or thing:

• The article made an allusion to the actor’s criminal past which annoyed him intensely.

• The book contained many allusions to the plays of Shakespeare which the majority of the children did not understand.

The noun illusion means a false or erroneous perception, impression or conception.

People can have an illusion, as well as create an illusion, in which case, they may either be creating art or attempting to deceive others:

• They are under the illusion that I am very wealthy.

• Rhonda hoped that well-chosen clothing and a heavy accent would create the illusion that she had recently arrived from Eastern Europe.