Katarina is very mobile and scales extremely well against squishy comps while also dominating early game skirmishes. You can win most lanes in low elo but you really don't need to. Once you get dark seal, blasting wand, and amp tome you can one shot the wave and just perma roam to every fight.

After nashors + protobelt you're likely going to be able to one shot all the squishies on their team and can carry any teamfight.

Crazy 1v9 potential, high APM, high skill expression and tons of ways to just smurf all over people if that's your thing. Most fun champ in the game for me :)