The Bizarro ninja are the weakest, most inept, least agile beings on the face of Bizarro World. They have many characteristics that can be described as 'un-ninja-y', but other than that can be whatever they want. Of course, since this is Bizarro World, they can only be the exact opposite of someone who exists in our world.
Bizarro ninja are tribal, helpful folk who will gladly give up anything to a random stranger. They are incapable of Bizarro killing another Bizarro human. They tend towards the simpler professions such as fishing and cooking over leatherworking and blacksmithing, and leave any battles that come up to Bizarro Aquaman, who 'am weaker than pre-Crisis Superman'. (Note: "Weaker" in Bizarro World means "stronger.") But I digress.
Bizarro ninja are wholly unremarkable combatants, and are often taunted by Real Aquaman. They tend to not fight anything more formidable than a cupcake. However, they make one exception: the grue. They can eat grues like popcorn, probably because ninjas can't eat grues at all. [disputed] But then again, Bizarro grues are the most timid creatures in Bizarro World, so that doesn't count for much.