you can make something like a giveaway game. Make for example 100 boxes. Hide prizes inside boxes and when I click the box, box opens and prize is shown. and if I won I get the prize. you can make like 0.001 bitcoin prize. 10 or 20 or 30 wining boxes depend how much you want to give away. or you can use some other altcoins for a prize like dogecoin for example.