Skarner is a very easy champion to play and fun, containing a single mechanic that lets you do the Jungle fields very easily.

In my opinion the best masteries to Skarner is the Grasp of the Undying, because at the end of the game you will get a great attack speed and a lot of life, causing them to become very strong in combat 1 vs. 1. You can also use the masterie Strength of the Ages, but know that your build should be focused more on tank items thus eliminating items such as Black Cleaver.

This build is geared so that you can use a lot of their skills making the passive Skarner is always active due to low recharge time of Fracture skill, as well as annoy enemies with the slow of Iceborn Gauntlet and armor reduction from the Black Cleaver.Isso makes Skarner is extremely strong in fighting 1 vs 1.

PROS:
EASY TO PLAY
VERY TANK IN LATE GAME
DOES THE JUNGLE CAMPS QUIKLY WITHOUT LOSING MUCH HEALTH AND MANA
HARD CC
GANK VERY EFFECTIVE

CONS:
YOUR ULTIMATE IS EASILY TO COUNTER
DO NOT HAVE AN ABILITY TO SHORTEN THE DISTANCE
YOUR SKILLS HAVE A VERY SHORT RANGE

Skarner shines in moments of team fights, with his ultimate ability combined with Fracture and Crystalline Exoskeleton can easily pick up a carry out positioning, ensuring an easy kill and a 5 fight vs. 4. It is easy to do if you have the summoner spell Flash but be very careful and choose your victim as well as the skill can be stopped by QuickSiver Sash or Mikael's Crucible.