I've heard a lot of complicated strategies for the lvl. 14 Ninja Champion (e.g., use 5 Meteors, then build 5 Temples really quickly to get 100 mana from Adoration, then use 1 more meteor), but they aren't really necessary, and it takes ungodly speed with a mouse to do that kind of thing anyway.
Just build 4 or 5 crypts around the left entrance to the map and let them level all the way up. Then, between waves 49 and 50, sell all the weaker towers so that the crypts will definitely hit the Ninja Champion first. Assuming your towers are strong enough (invest points in the Temple line of skills to boost Damage), they should all hit him more or less at once and he'll be dead within a few seconds. I didn't even need to use Meteors to finish him off.
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