Paul Hughes talks about that in this thread:also one question, how is resistance/immunity to weapon damage handled in the custom monster rules? I haven't found any notes about it.

Level Up (A5E) - Resistance/Immunity and CR
I was reading through the MM monster design rules because I am planning on doing some design, and I discovered that no accounting was made for resistances and immunities in CR calculations. is this intentional? I feel like at some point resistance and/or immunity sort of counts as higher than...
