I notice that WAKA is a little OP for novice to bronze because especially if the mana cap is 12 to 15 because some of the monsters are less life and the damaging effect of the poison is +2.
This is not a big surprise. Nowadays Waka Spiritblade is one of the most expensive cards in the game. It should be obvious that it is very effective in the lower leagues. Probably not many people will use this card in the lower leagues, because they easily reach the higher leagues.
Good luck and have fun.