Make sure you read the ruled for DARK DUEL ARENA before starting any matches.

Rule 1) Although both player's can duel under the requirements of a Challenge, only one duelist must.
(If one duelist isn't playing for Challenge Square, he/she must know that it is for Challenge Square.)

Rule 2) Your duel for Challenge Square will count towards your 1 duel per day for Dark Duel Arena.

Rule 3) If you win in Challenge Square, you will gain the said rewards, in addition to the regular rewards provided in Dark Duel Arena.

Rule 4) If you complete a Challenge, you cannot duel for that Challenge again under the same or lower difficulty (if available). If you re-duel a challenge, you will gain the difference in rewards of the current difficulty and highest difficulty completed.

Rule 5) If you break a rule provided within the individual challenge, your opponent will win automatically.