Skarner is a champ that requires some leech and spell vamp, hes fast and can hold anyone to dead, i will explain why i choose these equips and skills order.

I choose these runes because skarners skills are ap but ability power wont make that difference if you have 30 or 40 in the begining, but magic penetration does.
These runed are awesome in my point of view cuz i do high dmg with Crystalline Exoskeleton.

Well, masteries i can explain why i have defense masteries when im doing an offensive skarner.

Skarner need a little help at the begining, he needs some defense so he can go in the front line and kill some minions too and do some harras at the begining :P

These build, well i saw a build at mobafire i tested and i liked i have made some modification ofc.

Your base items will be Tear of the Goddess, mercurys treads and Sheen.

You probably will ask : "Why goddess tears first?", simple:
1º you need time to spam enough skill to get 1000 mana;
2º you will get mp regeneration, and believe me skarner use a lot of it.

While you are getting mp stacks you need to do the mercury treads, to get speed and resist, and finally sheen, sheen is the best item for skarner, with his spamable skill like crystal slash you can deal a good dmg every 3 sec.

You probably think that i get shen to late, maybe its true but you just need to hold a bit in line, till now i can asure you i have never got a problem with skarner even against caytlins and mf :P

Then after sheen, and after spaming crystal slash like hell (im allways doing, thank you mp reg :P), you need to finish Manamune, oh yeah, i allways get 160-170 ad when i finish manamune, and normalu i have only stack 600 mana :P.

NOw that we have manamune done we need speed, so Zeal is the ansewer, phage can come after you dont really need much hp for now because you have hp leech from Fracture :P; then finish Trinity Force

Now that we have done all the base items that skarner needs we have actually 2 choises, if the fight is getting really hard to handle and you die to fast i will give you the answer :P
warmogs armor
Believe me it helps like hell, spell vamp with hp reg on skarner is just wonderfull, if you still get a lot of dmg, if it is from ad just do a Randuin's Omen if it is ap you guys know the answer right? xDD yeah :P Force of Nature

Now if the you strong enough to be kicking the others butt, why not continue?, do a Hextech Gunblade, i can tell 80% of the cases im the first to enter the fight and leave alive :P
with this everything that skarner do will give him hp, imagine skarner in the mid of a team fight hes spaming skills like hell, because of his passive, getting an insane amount of hp and you team killing the others :P

Normally my games end when im doing the hextech gunblade (with a victory ofc :P) but when it gets a long battle, i do a warmogs armor so i can stay almost invencible and atmas impaler to stack with warmog and trinity hp.

Ok this is very easy,

Seismic Bastion > Ixtal's Impact > Shattered Earth > Shattered Earth > Ixtal's Impact > Seismic Bastion

Now the spells, well i use ghost and exhaust to have a continued harrassment, even knowing that skarner already have slow its not hard to fail it because we need to be too close to apply it.

I can tell that its rare the times someone run from skarner.

I allways do like this, first i try to slow them with my skill if i miss i use exhaust and then ghost, minions wont be in my way and even if the enemy try using flash i can allways chase him.

I hope you guys like these guide, its my first one im too newbie yet x'D, leave some comments.

And one thing skarner is not op :P