Movement speed Skarner (mostly played by Siv HD) has many pros, but gets countered by the most popular ad carries. Your main objective is to use all your items and run to the enemy carry and pull him in your team. If u get cc'd dont worry just use your mercurial scimitar and run like hell. If u have to go solo versus some toplane champ dont worry either just use your Yomuu's Ghostblade and deal tons of damage with your Trinity Force.

Pros:
-Pretty much unstopabble on his way to ult the carry with Mercurial Scimitar
-Some tankyness with Shurelia's Revire and Trinity Force
-High Damage output

Cons:
-Stuns, Snares and Cages counter him
-Hard to Ult a carry, who can jump or push you away (for example ezreal, vayne)

I didnt get any really tanky items into the bulid so I went really tanky in the runes and masteries. Runes are a combination of AD and some tankyness (dont forget about the movement speed).

Like above i didnt put up some really tanky items so i went almost full tank in the runes and masteries

I went crazy in here. Nice damage combined with the main objective movement speed, tenacity and some tankyness. Perfect combination with the very tanky runes and masteries.

If it comes to lategame, Skarner is the real carry for the team. He can go solo vs many toplaners and in teamfights u just activate all your items and run like hell to the enemy adc and pull him in your team. Its nice to have someone like fiddlesticks on your team, u pull the carry and when the duration of your ult ends, then fiddle comes with the fear, rest of the team deals the damages and carry is shutted down. For me the perfect team for Skarner is a fiddle on the jungle,
high damage ap carry mid like diana, Very high damage AD carry like Kog'maw and a support who has heal like taric.

Movement speed Skarner is a nice tactic. Well executed can lead your team to easy victory. Remember to save your Mercurial Scimitar for sticky situations like when u get stunned on your way to the carry.