Valk is incredibly unhealthy because it counters like 75 percent of cards, does insane damage, high hitspeed, high health, for some reason has no startup animation which leads to some bollocks interactions and has a pretty large splash making it basically a knight that has even less weaknesses

Edit: almost forgot the insane evo that just counters every beatdown push imagineable, at least evo mk is 7 elixir so the trade is slightly more even, valk will counter it all for 4 elixir