We are restricted to use lead, contact and account for marketing list.

In one of our implementations, we wanted to run Campaign and create marketing list on Credit Card Information of record (Contact), for which had to create a custom entity.

We could not use lead, contact and account as they were already being used for Sales portion of implementation. 

So we ended up writing marketing list on contact having 1 - n relationship with card custom entity. And we had to save and reuse the query used by User while creating the marketing list to identify the card records.