Skarner support is super useful at making their adc become a nobody and just ruin their game. If you play with an adc who also has cc or wants them to be closer to them, this works much much better. I duoed as pyke - skarner bot lane and we only lost lane 1/20 games, and also won most of our games because we can then roam into other lanes. The fact that your R can remove their adc from a fight and if they over extended then you just R then into tower and then its a 2v1 vs their support. Freelo.

I like to take aftershock so you get tankier when running at them. Runes aren't that important. If you have unflinching and celerity + water walking you are mostly set.

Chemtank is busted on skarner support. You used to have to rush righteous but the other stats weren't that nice. Now with chemtank you get tenacity, bami passive, health, armour, MR. Literally perfect. The rest of the build isn't really set in stone but I think deadmans and force of nature's movement speed buffs are nice.

I prefer W max because it gives movement speed and a shield which absorbs the first couple of autos when running at their adc. After that the extra slow from a high levelled E is pretty useful. Q isn't so important as you won't being doing damage anyway

Pretty much anything with range will be annoying to play into. If they have reliable cc even worse because you can't just run at them. Morgana and Sivir have spellshields so I normally ban them. This whole build works much better in a botlane duo because you can coordinate your all ins as well as get an adc that works with skarner support.