Ignore Resist vs. Weaken & Effective Guide by Mid (as of Patch 2.5)

I’m very interested in tests regarding these affixes. I would do them myself, but I don’t currently have the currency to do so.

Here is my input + further questions into the matter:
Effective is changing your element to be something that the monster is Normally weak against (I.E. if the monster was on a poison map (level 2), then no matter what type of damage you normally do, it’ll treat your damage as if it was shock). What happens though when a monster has greatly resist against the element that it’s supposed to be weak against (your above scenario). It feels like in this scenario effective will do nothing for you.

Next question:
I’m most curious how immunities come into play and if immunity can be broken with effective/weaken. That is, how is immunity coded?
Is it 100% resist? 200% resist? Or just straight up if (target damage = immunity type) then target damage = 0.
In the first two scenarios, immunity can be broken by a high enough weaken, in the last scenario weaken does nothing for you. Luckily Ascendance builds don’t suffer TOO much even in this case due to the prismatic nature which can deal damage that the monster is NOT immune against.