Monster and if implemented Pet arena/coliseum
Monster arena. I'm not going to hide anything here. I'm taking this idea right from where I know it. Dragon Quest/Warrior so if you have played pretty much any of the classic series you already know how it works. For those who don't it's pretty straight forward. You pretty much gamble on monsters who fight each other. The arena picks a monster or group of monsters to fight against a monster or group of monsters. In DQ/DW the fights and odds were pre programed but since this is a mmo the odds can be determined by the players. After the match is chosen players get to pick who they think will win. Then the odds are set and then you pick what side your betting on to win. The rest is basic. High odds = low pay out for winners. Low odds = big pay out for winners.
Pet arena. If a pet system is added where an arena is reasonable. ( Lets face it there's no point if the pet system doesn't let you grow and strengthen your pets in any way. Other wise it might as well be. Alright ready.... 1....2...3... flip that coin to see who wins... yay.
Again pretty straight forward except players chose to enter their pets into the arena. I suppose after that it can be like the monster arena except pet related prizes can be given to winners.
Could be neat