By default, Ninjas have 10 cost, 4 weight, and is repeatable.
Compare this to Blob, which is also 10 cost, 2 weight, and also repeatable.
Blob is an antag that delays a shuttle call and forces the crew to resist its tide, where the crew fights blob, and the blob, with its blobbernauts, fight crew.
Ninja is a single person running around causing mass hull breaches and forcing the shuttle to be called as soon as possible.
It also doesnt help that there’s no limit to when they can spawn, so a ninja can spawn 10 minutes into a round, causing a 20 minute shuttle call because there’s no atmos and he decapitated all of Security.
Another example is Bloodbrother.
Bloodbrother is 15 cost and 4 weight.
Bloodbrothers is 2-3 greytiders with the objective to steal 2 random items or kill 2 random crew members.
It’s completely unbalanced, and at least compared to Bloodbrother and Blob, Ninjas dont cause a round to be forced to end as soon as possible.
Having a ninja confirmed early is worse than a blob being confirmed early, because there’s nothing you can do against a ninja except hope Security eventually catches them.