(As always, I get these icons from the awesome site Game-icons.net, which has tons of amazing bits of art to use in games, completely free of charge! The "cards" I post here are proportioned such that they can be printed out at 2.75"x3.75", with 1/8" then trimmed around the edges to bring them to standard poker size...and I've now added dotted lines for the trim...)
Sylveon is a little more...I dunno, abstract(?) in the elemental sense...than previous Underground Elemental Beasts, since its Pokémon type is Fairy. That's not really an element. It's not even a quasi-element like Mind or something. But with an attack called Fairy Wind, Air seems like a reasonable element, doesn't it? So...that's what that icon up there is supposed to represent...the element of Air...weak to Air and resistant to Lightning.
One more note on Underground Elemental Beastfighting...I'm starting to play around with incorporating these into an RPG campaign and/or competitive game unto itself, so I also started playing around with cardbacks. Here's one of my first go's at it...
I hope everyone's 2017 has started out on the right track!