I have a Mac only, so I am not able to get Terraria through Steam. I was wondering if I can play Terraria on my iPad Mini with a friend who has it on his PC. I was wondering this, because I saw that Deepworld on iOS is compatible with the Mac version.
As for you mac,
I have three friends with macs, and over 50 friends with pc's who play Terraria. However, my three friends and I still manage to get together and play Terraria on my PC server using V-mare fusion. Using it, they launch windows on their mac, run steam on it, and then run terraria on steam. Its a great solution and as far I'm concerned it should work for you.
The best part is, that V-Mare might take some time to boot, but once its up you can slide between windows and your mac. Its simple!