#2. The Undertaker

Surprisingly, The Undertaker has also not been added to the WWE RAW Reunion show, considering he was on WWE television just a few weeks ago at Extreme Rules.
The RAW Reunion show could be the perfect place for The Deadman to set-up his next feud, which would eventually result in a match for the SummerSlam PPV, which will happen next month.
The Undertaker's last feud was against Shane McMahon and Drew McIntyre when he teamed up with Roman Reigns. I think that The Deadman could maybe have a feud with Elias, which WWE have been teasing for quite some time now.
Elias attacked Undertaker at Extreme Rules during the tag team match, while he has also teased a potential match with Undertaker in his various songs, where he has taken potshots at 'Taker. It would be an interesting match, one that would certainly help Elias' career.