You need to buy the game. Either on steam, or GoG. There's no profile to exchange, because someone will have to give up their entire library for one game, and that's a bloody stupid trade.
I don't think this is possible. Many people have more games than just Terraria on their Steam account, for instance I have 169 games other than Terraria. Terraria does not have a specific profile to go with it. It is only Steam and GoG.
Its goes on massive sales very often.
I believe it just became possible a few months ago.
First of all, it's ten dollars. I could go to the city and pick up that much money off the ground in an hour. Second, it goes on sale like twice a month and has gotten as low as 2 dollars, summer sales are coming up so I'd recommend then
