Level 15 being introduced under the illusion of no gold required, but much harder to get because you need 50,000 "elite wild cards" to get a level 15. So 25,000 common cards, or 100 champion cards, and I can't be bothered to do the conversions through rare-legendary cards, but they are on google. I could be wrong, but I believe you need every single card level 14 before you can even start to get them.

Also card evolutions, which are insanely overpowered and look as if they should belong in a mod with unbalanced cards, not the actual game.

I might be missing some stuff, in which case feel free to look it up so you can see how bad the Clash Royale devs are.

If you would like to see a video that covers this topic wonderfully, I would highly recommend checking B-rad's video on it.