Dear Remlap,
I actually like this idea of yours for Gangplank; please ignore the downvotes you've been given. I think it would be pretty cool to see him dressed in robes with a little emblem on the left-side chest area and a wand. Special ice-based magical-looking effects could activate whenever he slowed a foe with his Q or basic attacks, his ult could indeed rain fireballs down from the sky and I'd love to see what Riot could do with his W and E. Thanks for sharing this idea, hopefully it can gain enough support to get looked at.
Best regards,
Mr. Beane.