Is Skarner an ADC?

: I'm.... viable.......le...

: I'M! I'M VIABLE!!!

"No! You're not!"

"You're really not dude..."

Side note: I only see him played in jungle, I've seen him top lane once or twice.

Skarner is not an ADC.

A Juggernaut is a non-mobile pre-itemization heavyweight, that deals and can take significant damage. Unlike the other 4 listed, Skarner has a CC specialization in place of some of the class's usual damage.

It is kind of an interesting point, though, that the main juggernauts except Skarner really love high-AD builds.

(Though, Mordekaiser doesn't really crave AD much: he cares about completing his kit because his kit has ludicrous damage.)

The Juggernauts were intended as Top/Jg champs with decent gap closers, tanky, and tons of damage.

Skarner who?