You can theoretically make it to Challenger using any 1 champion.
That being said, it's much easier to have a group of champions that you use rather than just using 1 (although I've heard when climbing to plat, a lot of people find it easier to main 1 champion).
That being said, it's much easier to have a group of champions that you use rather than just using 1 (although I've heard when climbing to plat, a lot of people find it easier to main 1 champion).
Some people have made it pretty high up the ladder using only one champion i.e. Irelia Carries U, or Annie Bot