You level the Q before W to maximize your slow. This is a jungling guide, so you should be out ganking, and you won't do it effectively if you get kited and can't stick on target. Every rank in Crystal Slash is a 5% slow increase, compared to only a 2% speed increase with Crystalline Exoskeleton. In essence, you get more bang for your buck by leveling the Q first if you're looking for the ability to chase. For example, in my build, 1 rank of W will net you an 8.66 movement speed buff per level. Now, say you're against another Skarner using the same build. 1 extra rank of Q will get you 21.65 movement speed taken away from them. You gain MUCH more from leveling the Q over W in chase ability.

The masteries are actually the recommended ones from his Champion Spotlight, which I stated earlier in the guide. He isn't a heavy healing jungler like Nunu or Warwick, requiring him to build a little defensively to jungle efficiently. In addition to this, the masteries address his being "squishy" as you say. Building down straight attack, as I stated earlier in the guide, even with multiple different rune setups tried (armor pen, magic pen, attack speed, attack damage, ability power, armor quints, etc) ended up with about a 50/50 success rate after getting to red, and in an attempt to make it more efficient and keep him from dying to minions (which is not only embarrassing, but tells the opponents where you were and are probably going) in order to facilitate faster leveling and more ganks I chose the defensive masteries.

With a shield of almost 400 damage every time you W, you're not nearly as squishy as you'd think. Skarner's base defense stats are actually quite high, and this build gives 55% melee reduction and 45% magic damage reduction in addition to the shield. I also stated in the item section that you can swap out for more tanky items if required.

I'm not sure about leveling Q before W and also you're choice of masteries. And you are so squishy!

Yeah, I occasionally switch it up, but I don't really like Rylai's all that much on him since he already has a hefty AoE slow.

However, building him as an offtank I'll generally drop the Rageblade and Lichbane for a Sunfire Cape and Rylai's/Banshee's Veil.

I don't think there's anything really wrong with skarner except the movement speed on steroids should be alittle bit more powerful. he's really not imbalanced either way, try getting hextech over malady and rylai's over guinsoo's and he starts behaving a lot like Jax

Yeah, it wouldn't surprise me to see some changes come down the line, so I'll be fully prepared to change the guide, should it need it.

Its alright build but there buffing him thoe so be ready to change it there doing a remake
but +1