Can someone explain me, if I will make contest in my game with prize pool like LTC (user can choose other currency as well) worth 10 $ but users will not need to invest anything to play in this contest, is that legal?
Second thing, for beginning I need to make my game more popular, so I will pay those 10 $ from my pocket. Contest won't be only about best score, but about count of played games as well, so gamers will need to play it for example every day for one week. Question - does someone will play it to win contest?
I doubt if any government would prosecute you, if you offered a $10 reward for players in a game. There is also no gambling being done, so you do not have to register for a gambling license.
If you want to market your game, then you should offer some kind of referral system that would reward people, who recruit other people to play the game. You can fund this out of your own pocket in the beginning, but as your site traffic increase, you might attract some advertisers to fund this for you.