What are some of your favourite magic item combos for the big wizard that allow you do do sneaky, awesome, or unexpected things? My first thought was ethereal magic carpet flyer, but it seems as though Slann can't fly as they aren't "on foot".
Yeah, Slann can't use the magic carpet. My playgroup still let's me though I know I've used the hex scroll (turns opponent wizard into a frog) with some fairly hilarious results. Very situational though, and you can give it to a skink. Its not a slann specific item for doing ridiculous things.
Shadow Slann Egg of Quango isn't too bad for a dash of sneaky. Conspicuous absenses are sneaky. Against players well used to my playing style, I've left the Slann at home to make them waste their anti-magic purchases.
Ditto on leaving the Slann out. My opponents are waiting to see the big frog with all his magical might, then find themselves facing a much bigger army than they expected, headed by an Oldblood that's going to eat their face. Higher State: Oh no, your Hydra charged my Slann! How could I be so foolish as to leave him out in the open? Or maybe...your Hydra is now stuck in a combat he can't win, and I will Spirit Leech him out of existence. Ethereal combined with Arcane Unforging can lure a character into a useless charge, as well. Just keep supporting charges away so he doesn't go all Unstable on you, or give him BSB + War Banner.