Roar of the Slayer needs a nerf
Personally, I'm thinking Sion's E is a bit overpowered. Let's look at the facts.
Yes, it's got a pretty long cooldown, but that's basically the ONLY bad thing about it. 35 mp at all ranks is piddly. It's not stopped by minions (in fact it's HELPED by hitting a minion) does surprisingly large damage, especially if it hits a minion into the enemy, and it inflicts a huge slow. Not to mention how *fast *the skill comes out, reacting to it is nearly impossible without a dash of some sort.
Compare with Lissandra's Q: He can't throw it out nearly as often, but he's doing comparable damage before building AP and flat out better damage if you hit a minion with it (Lissandra will be trying to do this as well), costs him almost nothing, *and *it has outrageously better range for hitting a minion.