Hey Paul,  Yes the custom entity wouldnt show up on the left tree however if you create a relationship between your custom entity and contact or lead or account entity and sync down the field to marketo, you will see the field as an attribute under the person or company. From which you can filter your leads accordingly.  Cheers --D ... View more

Hey Heather, Just the sync user needs to have the marketo sync user role and not all the marketo users.  Thanks --D ... View more