There are a bunch of things that could be done with Ziggs to bring him back in line a tad. Mana costs, CDs, base damage. But I think that one of the best ways to make his kit less powerful is the nerf the duration of his Hexplosive Minefield (E). Right now, the minefield lasts 10 seconds. That's a really freaking long time. It's so long that with 40% CDR you can actually have 100% uptime on the mine field (9.6 second CD at 40%).
So, to tone down his zone control without changing the spammy AoE aspects of his kit, change the mine field to last less time, somewhere between 5 and 7 seconds.
Essentially, this will give champions and players more opportunities for counterplay against his mines. They can wait them out before making moves instead of simply needing to run through to get past. There will be downtime on the mines that people can use to make plays, as they should be able to.
