Also saw the Salem Witch today in a match, but my team were idiots and threw themselves at her and got eradicated. To be fair it seems at least half my team didn’t know about the halloween event and that the witch is deliberately OP. They thought it was bad matchmaking at the start.
Edit: Just got into a match with the witch on my side. Was fairly close but we won. Just me and the witch left at the end. I was in the red and the witch had maybe a third health left. She had 10 kills and I had 2. 
Reckon one have to focus her with HE from the start, although if the team is smart and protects her that might not be enough.