Hey Betcoin;) I'd like to hijack the question you asked another user about soccer competitions and offer some opinions. I took part in a lot of the competitions you offered in the past and I thought they were great (biggest winning parlays etc) but I guess you remember the feedback that it still benefits players who spam post a lot of parlays to win.

Prediction based contests are always the most popular, I've seen others do it and they get a LOT of participation but I understand also for the book, you want wagering also, otherwise no growth and no traction!

So have a prediction type contest, BUT to minimise a lot of spammers and fake accounts, WHILE also getting some volume from the competition, think about a mechanism that asks people to actually bet. This can either be charging users a nominal amount just for a chance to play OR giving players more entries for every amount wagered. E.g. Pay 0.1 mbtc to participate, or win 1 entry for every 1 mbtc bet on certain markets.

Alternatively, don't associate an entry fee but use something like your parlay contest but have like a whole campaign lasting maybe over 30 days. With last man standing to win a prize pool. Give people a week to sign up, and then once it starts, every day, to remain in the race, you must BET a certain amount AND WIN a certain amount, to progress to the next day.

e.g. Bet live or pre-match single or parlay a total of 2 mbtc a day. MUST also win 0.5 mbtc a day. After 30 days, all remaining players share a prize.