I had this idea to try Expose Weakness on a tank jungler like Nautilus. Since Naut is supposed to just lock down the target while the laner kills him, I figured Expose Weakness would be a no brainer. What do you think?
I can agree with that. The way I see it, since supports and jungles are essentially there to feed the rest of their team I don't see why you wouldn't take it. It would make ganks that much more punishing and worthwhile for your team. Plus hopefully it would reduce the chance of your jungler taking the kills. Of course I don't this applies to carry jungles like Xin.
If you're going thunderlords, I can see it, you have the space. If you're going SotA, you're trading expose weakness for Merciless and Dangerous Game. Not worth it, imo.
Isn't it in Ferocity though? I'd expect a tank jungler to be Resolve/Cunning since several of the old jungler-oriented masteries are in Cunning.
It's in a kind of weird spot being a Ferocity mastery that's oriented toward helping OTHER people deal damage, but I guess that's why Riot expects it to appeal to damage-ish supports 
that might be F/C or C/F but don't necessarily expect to personally 100-0 someone.
If I do go into ferocity tree as a jungler, I always get expose weakness, it's pretty much a given. It gives as much damage bonus to ALL your allies as you personaly get with double edged sword as melee without any drawbacks. So heck, why not?
Um the other mysteries don't do jack for tanks... so yeah
I really like this idea.
Quite a few tank junglers struggle with ganking because they don't deal a lot of damage, and those that are good at ganking aren't good for their damage.
Expose Weakness makes it so that they don't really need to deal a whole lot of damage in their ganks to have half-decent ganks.
Compared to the other tier 1 keystones in Ferocity and it seems like you have a very clear choice of which ones to use. You can go Expose Weakness for better ganks, Feast for extra jungle sustain, and Double-Edged Sword so that Lee Sin doesn't quite bully you out as hard.
