This is a great game and I'm happy to see an HTML5 port. However, let's be honest, if it wasn't for the ninja, this would be an idle game. You may was well call it Ninja Fear Slot Machine.
Overall a good game, great job. For me the first 7 levels have been far to easy. I completed them on hard the first or second time with almost no strategy. There appears to be a UI bug as tower upgrades don't appear in the text. For instance a fully upgraded air tower says Damage 14 when it actually puts out 17. Range upgrade is also clearly visible on the map, but doesn't show in the UI text. It would be nice to have more numbers, instead of 'stronger'.
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 "The Keeper Of 4 Elements"){kind=icon}