I think something simple, like drag and slide, near to a smarthphone lock or Osu slider with timer(10~20 seconds) would be good. If someone is not going to be able to drag it and slide he is going to take a penalty on damage and movement who is stacking with the time until he completes the captcha, when it reach on 5~10 times he is going to take a disconnect.
A drag and slide who is ‘‘transparent’’ who occupies something like 1/5
1/6 of the screen and need to be variable and grant maybe a 5% XP bonus for 20~30 minutes when you complete this captcha.
Obviously it’s a initial idea, just to start with something.
Got this idea from ‘‘Wakfu’’ Captcha. https://www.youtube.com/watch?v=nXg-XPmll8U
@Celestique was the one who suggest me to post my initial suggestion.
He posted another one with better overall explanation. A possible solution to the influx of bots on F2P release
*My photo editing aren’t even near to be bad, so please don’t blame for it being horrible. http://prntscr.com/agn56j (Obviously with more improvement .-.)