For scatter, scandium is used in light bulbs so maybe he will have a plug as a whip or as a tail. Light gray will be his color scheme and he may have some bulb-like protrusions from his back/shoulder. He will have that round turaga mask.
Leviathan will use the gunmetal black phantom mask. He will have a gunmetal color scheme and since titanium is used most commonly in razor blades so maybe he will have sharp blades against his arms/wrists and also titanium is used in jet engine gears, and turbines and such, so maybe he will have some jet engine/blaster things on his back.
Vanadium seems to be used in wrenches, so maybe he will have a giant wrench as a hammer/crowbar weapon? That sounds pretty cool! A dark silver color scheme will be granted to Zest! Also a silver firelord mask!
Chromium, as you know, is used commonly to beautify vehicles and other things made to be shinier. So…this character will have an insignia/car ornament on his chest or something? He will have a chrome and dark gray color scheme with a silver hau mask or maybe I will try and find a chrome one, but probably not.