Skarner shouldn't have been classified as Juggernaut, he should be classified as "Pain Train"
https://www.youtube.com/watch?v=AzUHaRsxFzg
The complete gang of "Pain Trains of mobile destruction and tanky annoyingness"

aka fighters that aren't quite tanks and aren't quite juggernauts and aren't exactly pure fighters
they do nothing but run around and cause the enemy to scream in anger and cry in defeat
no real on demand mobility in terms of dashes but plenty of high % MS boosts
they win by using a combination of mobility and anti-engage to just ruin your day
compared to the Juggernaut crew

Garen has a mobility move, but doesn't really play like a Volibear or an Udyr that have practically the same MS bonus. They use it their's for completely different reasons and purposes. They use it for intimidation and brawling, Garen just uses it because he likes spinning.
The Pain Trains all love skirmishing for the most part, but Juggernauts don't really. They all like to get rid of their opponent as fast as possible, whereas the Pain Trains enjoy toying with their opponent's first (for Singed and Udyrs, they REALLY love toying with the enemy before a kill)
If the Dunkmaster skins could all be put on Juggernauts, then American Football skins could be the "Pain Train" lineup for the Pain Train champions.