Send Consolidated Escalation Emails

I have a requirement to send consolidated escalation emails. One user can have multiple tasks assigned to him. But requirement is we cannot send individual escalation emails to users as its increasing their mail box volume. So Instead of default task escalation email,  I need to create a consolidated email which will show/inform all the tasks assigned to a particular user if task isn't completed within 2 days.

I have a task report I tried using grouping by task owner field but it isnt working , attached code image

Please help me with your ideas & solutions . Thanks in Advance