right now the WilloWisp does 1.25x damage for every Water, but its rounded down, so you need at least 4 Water to give you 2X. Though it goes up exponentially from there. We probably need to tweak Water a bit since its really hard to maintain a lot of water without it going away...that is on our balance to-do list!
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if you take the Wisp's base damage of 1 and multiplied by (1.25^4) the 4 is the number of waters.
meaning: 1.25x1.25x1.25x1.25 ends up being (2.44 but we round down to 2) 2X damage.
8 water would be 5X
12 waters would be 14X
18 waters would be 55X
24 waters would be 211X !! (but obviously its really hard to get 24 waters!)