Ignore Resist cancels Weaken & Effectiveness, so it can’t be used with them.
my Builds use Weaken +120% if I have at least 2 spaces to spare, and Ignore Resist if I only have 1 space to spare. even though a Crystal +90% Weaken takes up only one space and is actually better than Ignore Resist, if I can’t have Weaken for every attack, I’ll just lower my standards a little and use IR. now that I think about it, I tend to use IR for single Element Builds & Weaken with Prismatic or Ascendant Builds, so I have never really needed Effective Mythic.
I have only recently, maybe in the last few months, reconsidered using Weaken & Effectiveness together. I have done it before, but I usually don’t have room in my Builds for Effective Mythic. I think I’m going to test Weaken +90% & +120% & Effective Mythic and see if they make me happy or not.
here’s the guide. and he explains really well why Ignore Resist doesn’t work with Weaken or Effective Mythic. one of the Developers helped him with information, so it’s a really good guide.