How to retrieve Assignment Rules With package.xml
Syntax to retrieve assignment rules with package.xml
<?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
<types>
<name>AssignmentRule</name>
<members>Case.Custom Rules</members>
</types>
<version>62.0</version>
</Package>
Note: Use Object and Rule name in members. There is no limit in retrieving members.