Maybe! I do think there's been a plethora of Timelord big-bads already, so I'm hoping it's something new, personally.
*(Spoiler-y ahead)Looking back on it, since 11's timelord-less run, we've only had one season where the big bad wasn't the Master or some other timelord. I think we're due a change of pace.
I think it's the 'Boss' and they're building up an arc.
With the whole gold tooth thing I really hope it's not as obvious as The Master but who knows yet
It can't be The Master. They were in the tooth because the toymaker beat them.
Maybe another time lord? Rassilon or The Rani
Maybe! I do think there's been a plethora of Timelord big-bads already, so I'm hoping it's something new, personally.
*(Spoiler-y ahead)Looking back on it, since 11's timelord-less run, we've only had one season where the big bad wasn't the Master or some other timelord. I think we're due a change of pace.