Proximity Tangibility + Mana Drain is miserable for everyone, especially casters.

You are a ranged character. You are supposed to keep your distance.
So... you do.
However you are unable to do any damage because the mob is invincible. Naturally you decide to come closer. OH NO!
Oopsie doopsie. You now have zero mana because there is no way you can kill the rare before it can drain all your mana.

Then what are you supposed to do? Autoattack it to death?
What if you have some nondamaging ability on your caster weapon?

The combo of these two together is simply insufferable and basically kills any chance of you progressing.
Now imagine this on higher level maps. For better enjoyment, this combo has to be changed and disabled.

There is a difference between difficulty and unfair bullshit.

One year later...still there.