Nrsimha Purana is not one of the eighteen Puranas, but is one of the upa-puranas, or auxiliary Puranas. It is quite definitely a Purana in the mode of goodness, or a Vaisanva Purana, because from beginning to end it is nothing but glorification of Lord Visnu and His innumerable forms, one of which is Lord Nrsimha, as well as glorification of the Lord’s devotees, as well as His devotional service.
A major portion of the Nrsimha Purana is taken up by summary descriptions of the dasa-avatara, or ten major pastimes incarnations of the Lord. Here the pastimes of Lord Ramacandra are described in greater detail than those of the other incarnations, so that is a kind of mini-Ramayana.
The pastimes of Lord Nrsimhadeva are not told very elaborately, but there are many additional details found in this rendition. Nrsimha Purana is a very short work compared to other Puranas but the advantage there is that the stories are told in a concise manner and do not ramble on and on.