Went into the lab to test the numbers on Grave Rot. My results:
Grave Rot: 1% per tick. Will hit up to 9 times (tested by walking straight into opponent)
MB Grave Rot: 2.5% per tick. Will hit up to 9 times (tested the same way)
Old BnB (1,1,2,MB SH, j2, b1,Trait)
28% + Normal Trait (25% or 31% or 21%)
Max Damage: 59% for 1 Bar
New BnB with Grave Rot instead of j2
23% + GR Trait (33% or 35% or 27%)
Max Damage: 58% for 1 Bar
If you're going for the Power or Chip Traits and only want to spend one bar, replace the j2 with Grave Rot for slightly more damage.
Background Interactible BnB (1,1,2,IO,b3,j2,1,MB SH,j2,b1,Trait)
40% + Normal Trait (25% or 31% or 21%)
Max Damage: 71% for 1 Bar
Background Interactible BnB with Grave Rot instead of j2
37% + GR Trait (33% or 35% or 27%)
Max Damage: 72% for 1 Bar
Go for the Grave Rot no matter which chain you're going for, it does more damage.
2-Bar MB GR (1,1,2,MB SH,MB GR,j2,b1,Trait)
30% or 32% + Trait (41% or 41% or 32%)
Max Damage: 73% for 2 Bars
This is slightly improved damage over the current 2-Bar combo (1,1,2,MB Dead Air, b1,MB SH,j2,b1,Trait) and it doesn't switch sides with the opponent.
If any of my numbers are off, or the pre-patch combos without Grave Rot were more damaging please correct me.