For the All-Days Arena Bonus Event, the Autumn Equinox Event Part 2 announcement erroneously stated that each of the All-Days Arena dungeons would be available at 1/2 the Stamina cost.
The correct All-Days Arena Bonus Event content is as follows:
Monday - Friday Arena dungeons: Rare dragons guaranteed to invade
Saturday & Sunday Arena dungeons: 1/2 Stamina cost
Players who entered these dungeons during the Bonus Event prior to this announcement will be compensated in Magic Stones equivalent the Stamina expenditure.
We apologize for any confusion this may have caused and thank you for enjoying Puzzle & Dragons.