Skarner Health Issues
I have played a decent amount of Skarner, and I'm not going to say I'm an expert on him, but in playing him I feel like there are some things that can be worked on.
My main issue I have while playing him right now is that his E feels inconsistant. In the current state, if you land e then auto directly after, even if E's damage applies first, the stun won't go off. I feel like if you're casting your E before you auto attack, it should stun.
Secondly, the crystals lead into a larger feast or famine issue, which is something Riot has worked very hard to eliminate. Jungle as a whole when your team is behind gets punished hard, but the fact that your clear becomes very slow unless you notify the enemy team of your location (capturing a crystal), is a problem. Skarner has too much power ties to small areas of the map.
The first one should be an easy fix, just make the travel time at point blank of E faster, so it's more constantly applying before the first auto. The second issue is a little trickier, but I feel like toning down the crystal's power a little bit, and then tying more of it to the E.
For example, if you land Skarner's E it crystallizes the enemy, granting you the bonus effects of the passive, and then persists for 1.5 seconds after stunning them.
This change would allow Skarner to be a little more consistent with his power, and make his e feel more meaningful and be a more powerful chase tool.
I do like the crystals, as they give Skarner a unique identity, but as is, the window you can gain the bonuses from your e when not inside them, can make you feel helpless when chasing down enemies. I don't think this would be too powerful, but shaving some power off the shield or q to balance would make Skarner feel more cohesive as a whole.