Samira appears to be the final new champion (and 151st overall) teased by Riot earlier this year: she’s rumored to be a marksman but also to have assassin-like abilities, including an ult that’s described as “jaw-dropping.”
Pretty good summary of what’s known so far:
I like her already because the mysterious emote above reminds me of 
HERE SHE IS!
Official splash art!
Abilities rundown: https://na.leagueoflegends.com/en-us/event/samira-abilities-rundown/
Taunt skillshot
I read about this yesterday – I think it’s awesome, but I’m waiting for the first vid of someone getting killed while doing this 
Bayonetta vibes 
Flash warning
Samira MIGHT be just a wee bit OP …
Forgot to mention that I played her for the first time yesterday … and she is indeed quite OP. (Her passive, in particular, is kind of brain-dead.) I went 14-1-10 in my first match ever with her …
)