Magic Penetration

Since the primary focus is on AP rather than AD or AS, you may still want to consider having AD to do any final blows. This statistic will benefit you more in the later part of the game.


Movement

Optomization for this attribute depends on maximizing your movement speed * 4.5% modifier.
We can replace 'Boots Of Swiftness' with 'Mercury's Treads' since the modifier boost is picked up by the 'Lich Bane' and maximizes the +35 tenacity and grants +25 magic resistance.


Ability Power

This will grant your summoner some initial AP which is not much and could just as easily be swapped out for health regeneration to compensate for whatever minor initial damage you might take. To make efforts in compensating for Skarner's bad starting handicap, your best offensive skill is a ranged one, Fracture.

OFFENSIVE
Increase your ability power 0.6 per level from Archmage's Savvy.

Increase your critical strike chance 0.66 per level. (insignificant but required to get to the movement bonus tier)

Cooldown Reduction of your abilities by 3% from Sorcery. This is required for early game play until you have acquired the 'Morello's Evil Tome' and 'Frozen Heart'. The cap is 40% CDR, and this attribute will be absorbed later on by the 2x items each yielding 20% CDR.

We want the 15% magic penetration modifier coupled from your rune's stacked initial +14 magic penetration bonus modifier and any items you acquire in game. There is no hardcap, only a softcap which peaks at 49% as there are no items in game that will theoretically allow you to reach beyond this. The 'Void Staff' would have had to have been included as part of your build as well.
1 - (0.6 * 0.85) = 0.49


DEFENSIVE
Increase your magic resistance by +6 from Resistance. The more the better.

Increase your armor by +6 from Hardiness. This will also be added to the items you will buy later on.

Increase your health regeneration 1% of your maximum mana from Strength Of Spirit. Since you are going to be building a mana pool from the 'Tear Of The Goddess', this will play a significant role.

Since we care less about dodge and that you have 0 attribute, the movement tier bonus after dodging an attack will be useless. We can absorb damage with the armor to compensate for this. Focus putting your skill points on areas that will be beneficial to your champion.

-2 damage from minons or monsters from Defensive Mastery.

Block 1.5 physical damage from Harden Skin.

Increase your HP by +48 from Veteran's Scars. The more the better.

Gain 4% attack speed from Ardor. (insignificant but required to get to the movement bonus tier)

Decrease all damage being dealt to you an additional 4% from Tenacity. This is greatly significant and beneficial later in the game and includes magic & melee damage.

Give this build-guide an ample chance of at least 3 games before you make your decision if it is a good one or not.

- This will be critical in early game play, since this champion is practically worthless against ranged attackers especially when lanning. These boots will help you run to safety by either out running the enemy or matching their starting items which will keep them from advancing upon you. Your Quintessences give you a 4.5% speed advantage, so you should be guaranteed an escape.
- Skarner is mana deprived and he has the constant ability to spam spells. This and the cooldown reduction make this pairing a perfect combination. It is a small investment and must be rushed in order to accumulate your mana pool. Spam spells while regenerating at your fountain (base) to increase the maximum mana threshold.
- You will need all the magic resistance you can get along with armor. This will give you the +35 maximum tenacity that you will need and provide you with additional magic resistance to fend against AP attacks.
- Your movement speed is good for a few levels to help you in running to safety, but you NEED tankyness. Health is a must, and this is the game changer right here. By getting this early on, ensures your champions longevity within the game and can obtain kills faster which will provide you with gold to keep the advantage of maintaining your build of new items over your opponents. I would suggest that you get this item immediately after Tear of the Goddess.
- This item will increase your mana pool and provide you with the necessary armor to fed against auto attacks. It is going to provide you with the necessary cooldown reduction you need early game to sustain your ability spamming combos.
- Increases your mana regeneration in between creep waves as well as when moving across the map. This also provides your champion an additional 10% cooldown reduction as well as giving him more ability power critical to this build guide.
- Upgrade your Fiendish Codex, which increases your cooldown reduction and amplifies your mana regeneration rate and is imperative since we are not building an ArchAngel's Staff. This will also upgrade your ability power as well.
- Will effectively slow your opponents when using your AP spells. This is needed as CC persists and your teammates get out from their lanes to help support other team members. This item helps upgrade your HP, and AP which is going to be required for mid game play.
- Increase your CC which is probably the best item for your build. It not only maximizes your cooldown reduction, but it will slow the enemy's attack speeds from dealing damage to you. The increase of armor is also granted, allowing you to sustain more damage from other incoming attacks as well as tanking and diving turrets.
- Increase your AP and deal damage to building structures that are incredible. The movement speed increase will stack with your Quintessences and Crystalline Exoskeleton ability. The additional mana will also increase your maximum mana pool. This will be required to help your mana pool as your next item forces you to sell the Tear Of The Goddess, which cuts your mana base down by 1/2 now. This is not as much of an issue at this part of the game, because you do not need to use as much mana whereas previously for farming and other things.
- The 15 spell vamp is ideal for regenerating your HP while out in the field. If you take damage, you can simpily go kill a few creeps to replenish your HP rather than recalling back to base. At this part of the game, recalling takes time and the walk back is long. You should still have enough mana to do what you need to do and this solves your HP problem. Attacking the opponents benefits from this slightly but do not rely on it like it is a Bloodthirster. This is not what it is intended for. Your main goal is to provide additional team items for spell vamp they can benefit from.
- Grants additional AP and gives your team 25% spell vamp. This will greatly benefit your team in not only being able to take down Barron without suffering hardly any damage, but to sustain team fights thus ensuring you victory.

The skill ordering is non-negotiable.

Your first skill is either your Crystal Slash or your Fracture spell. You want to maximize your Crystal Slash early as requirement for this champion. This will help with farming lanes and slowing your opponents movement when in range.

Your ranged spell ability is Fracture. This is good to be able to do damage from a distance and should also be maintained. By mid-game, you should have had both your Crystal Slash and your Fracture spells maximized.

You can rely on only having 1 point on Crystalline Exoskeleton for a majority of the game as movement & attack speed bonus ability.

As with all champions, get your ultimate at level 6 in case you need to use it. It works good early game, especially when dragging your enemy's into your turrets for an easy kill.

- Will allow you to get back into where you left off, after recalling back to base. Also is good to push lanes while the rest of your team has the enemy distracted. This in conjunction with your Lich Bane item will allow you to creep in and knock down the opponents building structures in no time.
- This spell is used to get out of a jam in a flash. Many of times, while pushing lanes solo.. the enemy will try to gank you. Flashing over a wall is usually the best way to escape their stuns/slows. You can not rely on anybody but yourself for help and this can hopefully get you out of range long enough to rely on your movement speed bonuses and escape to safety. Use this spell in conjunction with your ultimate so that you can cover more ground when dragging your enemy back into your posse for meltdown.

If you see a team mate running being followed by the enemy, your Crystal Slash will slow the enemy on second cast if is in range.

If you see a team mate running your ultimate WILL save them as well. Use it to drag the enemy in the opposite direction.

If your team is sharp and witty, you can drag the enemy back into your posse while they melt him.

Crystalline Ghost Drag
Use your 2nd ability, Crystalline Exoskeleton, before you perform your ultimate Impale. This way you get the speed movement bonus to cover more ground during activation time of your ultimate. For options of having Ghost as one of your spell options, you can try this method to compound your speed movement bonus. I prefer a different method completely as listed below.

Flash Impaler
To be used in conjunction with the aforementioned.
When you grapple your enemy, flash to where your team is for meltdown. Even more efficiently, if you have Lee Sin on your team, he can blast you clear across the screen along with your target victim. You can then flash an additional portion of the way, including walls.

Don't forget to use your red potions, and make it a habit to use it as soon as you take damage rather than when your HP is real low.

Use your ultimate to drag enemy into your Tower and Lazer for immediate death.

Pros

Skarner's ultimate is one of the most fun, especially when combined with ghost or flash and his Crystalline Exoskeleton spell.
He can mow down minions like a lawn mower.
At about level 6, you are constantly casting at least one of you spells and it provides a fun aspect to this champion.
Everyone under-estimates Skarner.
Teammates will love you because of your support items, CC, and tankyness.
A good overall champion that is fun to play and is good for farming lanes and taking down towers.

Cons

Not as much damage as one would expect.
Early game is weak, and spell damage is practically nil.