They stack additively so if you had 30x on both it would end up a 60x multiplier overall. I want to re-do power 8 but I'm working on fixing the regular economy imbalances first. I'm going to add little monsters to fight in between the bosses so power 8 would help you earn more coins from those monsters. In my grand plan you unlock the 8th column and only need to get to level ~91 to beat the game and then using 8's power you progress to level 100 where you can prestige and start story 2.
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They stack additively so if you had 30x on both it would end up a 60x multiplier overall. I want to re-do power 8 but I'm working on fixing the regular economy imbalances first. I'm going to add little monsters to fight in between the bosses so power 8 would help you earn more coins from those monsters. In my grand plan you unlock the 8th column and only need to get to level ~91 to beat the game and then using 8's power you progress to level 100 where you can prestige and start story 2.