The mask and pen tools under opacity in the Effects Control panel are missing.

You cannot work as before ... so go to the Tools bar in the Timeline panel, hover over the icons there for Ripple and whatnot ... when you hover over the new icon for masking, you get a pop-up that gives a link over to their documentation on the new masking system.

It is far more powerful, but ... you cannot figure it out unless you read the documentation.