hmm, i don't really agree with these suggestions.
- i don't like buffing the passive cos ziggs should be really weak when you close the gap so giving him that extra dmg is a bad idea
- he got mana cost buffs not long ago and mana is one of the ways of gating poke champions so that's imo ok
- karthus q paradigm for his q sounds counteractive to his blow shit up personality. if anything, it should be the opposite, it should promote hitting multiple targets, not just one.
- shorter w cd is a big no cos that's his escape so you give him too much safety when ziggs shouldn't have so
- spells dmg turrets is something that's also a big no since his q has like 1400 range lol
i feel like a fun buff could be that his q has a larger aoe area if it hits a champion or something like that, but tbh i don't really think ziggs has big problems, his winrate isn't terrible and he's picked often enough and he seems to have pretty decent strengths and weaknesses.
he's a poke and zone control champion. his e is a strong as hell spell and if he gets farmed his poke is really strong too. he pays for that through low mobility, tho he has a simple escape in case someone gets to him, and with limited cc.
i think his numbers right now are pretty good and he's mostly struggling with the meta like pretty much every other low utility mid champion that's not ahri