> In Cartoons (and in science), wasn't this called Planet X and in other hypothesis 'Nemesis'?

Nemesis is a hypothetical star, not Planet 9/X, explaining different phenomena; it would be farther out.

But, yes, Planet 9 is more recent name for the same hypothetical object as Planet X:

https://solarsystem.nasa.gov/planets/hypothetical-planet-x/i...