They are called Ddakji (or Ttakji). I have no idea how either are correctly pronounced, but they are rooted in a traditional tabletop game with cardboard discs. Westerners would best recognize traditional Ddakji as something like P.O.G.S. without the metal slammers. Kids would merely take a cardboard piece and slam it crazy-hard down on others to try to flip them over.
Alternatively, rubber Ddakji found themselves on toy shelves as well, replacing the small thin discs for large, hand-size, rubber cut-outs of popular characters, with the exact same rules: whack your opponents Ddakji so hard with your Ddakji that theirs flips and lands on the opposite side.
I'm personally drawn into these guys, but then again, virtually anything neon, transparent, glittered, and slug-casted will always know how to get my wallet lighter. Although I don't have the budget into being a serious Ddakji collector, I would love to have a a good amount around, if nothing else than to have a few drunk Ddakji games with friends.
I just recently learned of their existence and currently in the works of picking up some. I'll do a hands-on review in the future when I get to slam them around myself, maybe even intoxicated.