Shell talismans kill Grim Reaper Eddie dead. Just about every Grim Reaper build is a glass cannon. He bounces off of the Shell talismans (and high HP Sentinel characters) and then gets crushed.
But yeah, I've seen teams involving a Grim Reaper, a Nomad, and a Red Bat, and they'll vaporize a couple of your toons if they go first if you're not prepared.