All your FAQ's on the Mac port are answered right here. Can you play with PC players? Will your characters transfer? Is there mod support? Yes to all of these. Find out more: http://www.torchlight2game.com/news/2015/02/02/tl2-mac-port-now-available-from-steam/
Torchlight II | Big News!
Last but not least, we want to thank all of the people who have been patiently waiting for the Mac port to be released. We hope you enjoy it! Go get it now!