The new items they added make killing the Grim Reaper pretty easy now
You have Infinite Corridor (Clock Lancet + the 2 ring halves you find on the stage) and Shrouded Cloak (Laurel + the 2 cloak halves you find on the stage)
Infinite Corridor isn't very useful for trash, but it is for the Reaper. It removes half the HP of the mob with every attack and it does this attack pretty frequently. You still get the clock lancet effect as well, so you can freeze the reaper. So the 1 Billion HP reaper becomes 500m, then 250M, and so on and so forth. If you have good attack items that do really good damage, you're more or less guaranteed to kill the reaper in under 2 minutes. After you kill the reaper, a white reaper appears and basically instantly kills you once it catches you (you can't outrun it, even on a max speed red death)
The Cloak caps incoming damage at 10 and also still gives you the laurel charges