These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
That one is the most well-known, but they're all good, you can find them all here.
Goddamned Bats: The weakest enemy, a uniformed trooper with a knife, comes at you in swarms. Leter on they start wising up to your ninja, and will utilize flying kicks to attack you.
Gray ninjas will keep jumping around your character, and are hard to hit. To defeat them, let them jump over you, then attack them from behind when they land.