@manofmysteryrmthe DMG custom monster rules confuse me. How do you calculate the offensive CR of an ability like gelatinous cube’s engulf it's more art than science, but as a rule of thumb I'd halve any future damage that can be avoided with a check or save

— Mike Mearls (@mikemearls) August 11, 2015

@manofmysteryrm for something like the cube, its final CR quite likely owes more to playtesting than applying offensive and defensive CR

— Mike Mearls (@mikemearls) August 11, 2015

@manofmysteryrmwhat do you mean by future damage? Ongoing effects like the engulf, or future as in how you calculate damage now on?
damage I might take because of something a critter did, but on my turn I have the chance to act to avoid it

— Mike Mearls (@mikemearls) August 11, 2015