Hello, I am FrozenLeprechaun and I love Scorpions and Skarner. Go figure. Now I know my build is very expensive and requires a lot of work. That is why I will keep updating this guide as I get constructive criticism and feedback on how to build him the most optimal way, then we can all have a good guide to refer too.

Red: Flat Damage. The flat damage increases your plain attack damage and the damage on your Q, making it a good choice for the jungle to kill things faster of course. I wouldn't suggest getting ARP because I do not think it affects his Q. Which is what I rely on in this build for the majority of my damage, and the slow of course.

Yellow: Armor. Your jungling, did you expect another yellow?

Blue: Attack speed. More CDR, Help with clearing jungle faster. And more dps.
Or: Magic Resist per level: Skarner is quite squishy with this build and having some Magic Resist is very helpful for when you finally leave the jungle and start ganking/team fighting late game. The choice is yours.

Quint: Flat Ability Power. Buffs all your abilities. Helps quite a bit.

I know my Mastery set up is a mess but I like how it works.
Skarner has no gap closer and is susceptible to CC, so he needs a lot of movement speed. That is why I go that deep into Support.

I then build into defense because... I can't clear blue buff solo as him with offense/support AT ALL.

And obviously I get the smite mastery because it helps quite a bit.

This build is DAMN expensive but the items you get while building toward the meta items still make a big difference on your damage.

He is very spammy and benefits from everything on Trinity Force except the crit, even then, it's not too bad to have.

The gunblade is one of if not THE best hybrid item ingame, and is extremely useful for Skarner, the use is AMAZING, considering his slow's range is cancelled if your 5 units away. If your chasing by right clicking on a person, you will almost never land your slow.

The wriggles is good for his jungling and you can ward one of the lanes to help your teammates even more.

Guinsoo's is an all out good item for Skarner as he could use the Atk speed for CDR, Ability power and atk damage.

Guardian angel will give you all out defense that by end game, the enemy should realize that your a pretty big threat if not shut down with CC or killed.

The Good:
Flash is plain out good. I never go without it on anyone, it's just so useful for getting away, around, and engaging, whether for your ulti or w/e.

Smite, since your jungling is a must.

Ghost is useful too because you can use it as an escape mechanism and you can ulti then ghost, and pull them further than you originally could. (I wouldn't recommend using it over flash.)

Exhaust, he needs this for a ranged slow when chasing or just weakening a foe, it is extremely useful for him considering his slows range is absurdly small.

Ignite, not bad for the damage and healing reduction but I personally wouldn't take it.

The Bad:
Fortify, unless your getting the mastery it's near useless, plus it's just not the right spell for Skarner.

Revive, only good on the old Pantheon where you could engage in a team fight, die, revive and skyfall into the middle of the team.

Teleport, not bad but I wouldn't sacrifice an escape mechanism or exhaust/smite for it.

Clarity, his mana problems aren't existent when you have blue. And without it, sheen still gives you a nice amount to deal with and should be fine on mana from there onward.

The Ugly:

Clairvoyance: He's not a support and doesn't have a long range gap closer like Blitzcrank.

Rally: Terrible ability, bonus is hardly noticeable, it's weak and can be screwed over just by kiting the champion away from it.

Heal: Horrible, just horrible ability, the heal is only good early game and scales terrible into late game. It's for noobs who don't know the potential of the other abilities, don't take it.

Basically, Skarner being a beefy, fairly slow (without using his god given speed boosts) and a champion with no gap closer, while being susceptible to CC. He needs his movement speed buffs, extra beefyness and CC mitigation from Merc Treads. Him being a VERY item dependent champion, he is fairly week early game and slowly gets A LOT more powerful throughout the game.

No info on this yet as I have not dared try ranked as him yet.

Pros:
Good DPS.
Fairly good Burst.
Isn't bad when built AP, AD or Hybrid.

Cons:
Fairly slow for not having a Gap closer.
Ulti and Q range is melee and no longer.
Susceptible to CC.

When jungling just start follow the regular route of...
Blue>Wolves>Wraiths>Golems
B and buy boots, preparing for gank at lvl 4.
Pick up red and head for a gank.

Then just continue ganks and jungling while placing your ward from wriggles(Obviously).

For team work, you can either engage with a speed drag into allies. Wait for someone to engage first and then just start ripping them to pieces and use your drag to pull people off of your AD carry in team fights. Your ulti interrupts other Suppresses, so if you see warwick or malz using theirs, you can interrupt it with IMPALE.

Skarners unique abilities work in-twine very well. If you E and then Q, you gain healing from the majority of marks. Popping his W makes all his abilities cooldowns shorter (In theory). His ulti is great for grabbing prey and dragging them into tower, grab retreating divers into tower. Grab retreating opponents period.

One thing I have found from much practice as him is that if you are chasing someone just by right clicking them, with no assistance and/or CC currently on them, your Q is not going to slow. So your going to have to get beside/closer than you would be in auto attack range to be able to slow them down.