Totally want to see some skin love for some of these champions, so here's a copy+paste of one of my responses to another of these posts.
Skin suggestions:
Udyr -- a snow theme. Snow Leopard, Frostbird, Water Turtle(because cold-blooded reptile)?
Skarner -- a water skin? Or maybe toy Skarner.
Xerath -- maybe an infested version or a dark star version. Maybe could be Odyssey or SG villain skin.
Shaco -- what about a more kid-friendly version? His traps spray water at enemies, his E shoots water balloons. What player wouldn't want access to heat-seeking/homing water balloons?
Mordekaiser -- a wooden version hasn't been done yet, right?
Rek'Sai -- how about a 'stuffed animal' version...make her look like a soft toy.
Nunu and WIllump -- might as well give us a dangerously high temperature version, we have Frostfire Annie after all. Imagine how scary Willump would look if rolling a ball of fire across the battlefield.
Kassadin -- a water or a snow skin? Or a Golem(kind of like an alternative to mech/cyborg) version of him.
Maokai -- a water or snow skin, or a mech Maokai.
Vel'Koz -- a water skin, or a boss/arcade skin, or Odyssey/SG villain skin.
Sion -- pillow fighter Sion or maybe a cyborg(Project Sion) or Odyssey skin.
Nocturne -- I don't know what to suggest here because I feel like he could use a visual rework.
Shyvana -- how about a lightning dragon skin?
Kindred -- what about a druid and pillager skin? Lamb is the tree hugger, and wolf molests nature. Does that work?
Volibear -- how about a cyborg Volibear(Project Volibear) or a mechanical Volibear? AFAIK we don't have one. Can also give him the 'stuffed animal' skin like with Rek'Sai.
Taric -- would love to see him with amber-colored gems. Or perhaps the gems themselves are real amber. Either way, would look awesome I expect.
Ryze -- make him be a tool user. Like Batman or whatever. Him relying on physical things instead of magical would be funny. Maybe he could look like a forest ranger or something.
Kalista -- toy or cyborg Kalista would be cool I guess. Golem Kalista(made of wood or stone or whatever) would be interesting as well.