Oh, Mona Vanderwaal, we barely knew ye! That's not true at all, is it? As Pretty Little Liars resident evil genius, Mona was the original 'A' at the end of season 1 and has proved herself in the subsequent seasons to be a valuable (if impossible to predict or even fully trust) ally for the girls to have. Let's all pour one out in memory of Mona, who was killed off last night in bloody, awful way.
We've lost characters before on the show, but it's never been so definitive. I think that's what was hardest about Mona's death last night -- you know that sister-friend is dead, and there is no way she is coming back. That said, Mona's death has kind of kicked the show back into high-gear. While 'A' has always put the girls in danger and bothered them with threats, this is actually the first time she (or he) has taken one of their lives. That is some heavy nonsense, yo. But why did it have to be Mona?!