How does this Item Build benefit Skarner?:

Spirit of the Spectral Wraith-
It adds more Ability Power to Skarner to make his Abilities more powerful in fighting. The included cooldown reduction helps with making Skarner be able to use Crystal Slash faster to take down groups of minions and neutral monsters. The faster cooldown of Smite, and 30% more damage to Monsters will be able to make Skarner easily and quickly take down neutral monsters a lot more quicker. It'll also help for taking down Super Minions more quickly. The combo from the 20% Spell Vamp and Fracture's marking passive will be able to make Skarner be able to heal health while fighting Wraiths and Wolves.

Stinger, Wit's End, Lich Bane-
All three of these items of interesting Unique Passives where it'll give magic damage bonuses to Skarner's basic attacks. The Stinger and Wit's End will give the neccesary attack speed Skarner that when combined with Crystalline Exoskeleton it'll be a very good bonus for fighting in late game. The huge magic damage bonus to Skarner's basic attacks will make his basic attacks do very good damage when you have all three of the items. With all of the attack speed, you'll be able to use Crystal Slash practically every 1.5 seconds when fighting, and also meanwhile in between of the cooldowns of Crystal Slash you will be doing high damage with your basic attacks. All in all, having the Stinger, Wit's End, and also the Lich Bane in your build combined with Crystal Slash you'll have very high damage per second when fighting.

Void Staff-
The Void Staff gives a great bonus of 70 Ability Power to Skarner to make his abilities deal tons of more damage. Combining the power of Ability Power and also the passive of ignoring 35% of your enemy's Magic Resist, you can deal major damage to squishy champions on the other team. The great Magic Penetration from this item's passive also works well with Lich Bane's passive called Spell Sword. Making your basic attacks hurt champions who do not build up on Magic Resist do a lot more damage than usual.

Ionian Boots of Lucidity + Alacrity Enchantment-
The 45+ Movement Speed and the 15+ Alacrity will give Skarner enough Movement Speed to chase down most champions who do not have Boots of Swiftness on them. Making Skarner be able to chase down weakened champions while using Crystal Slash to slowly kill them as they're running away.

The Runes of Scaling Ability Power will be to make sure that Skarner will be able to have good Ability Power bonuses in late game if you haven't been neutral monsters in the jungle well for money or either you're having trouble getting the items you'll need for more Ability Power by having being invaded more than once in a game.

These Masteries for Jungle Skarner are basically for making Skarner very offensive when it comes to fighting. The Offensive Masteries that should be used should be able to give a good portion of Ability Power strength throughout the game to help you slightly be more better in fights.

Inside the Utility Masteries the fully upgraded Wanderer Mastery should be able to give Skarner a good Movement Speed of 352 in the beginning of a game making it faster than most other champions if they don't start with boots. The good early +3 Mana Regen should be sure to give Skarner an impressive 16+ Mana Regen right after he gets the blue buff. The Mana per Level Mastery should be able to take care of Mana Problems in late game.