Balance
With the upgrades, you will need to balance both sides of the trees if you wish to beat the ending. You'll need to upgrade both the close range scythe attacks, as well as the long range cross attacks. At the end, you'll have to resort to one without the other, and then vise versa soon after. If one is left un-upgraded, you're going to have a very hard time beating the final boss in this game.
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