The progressive cap (Level 59, but with Rare Candies to 59, 61, etc. as you go) provides the most authentic "Hardcore" experience. It honors the difficulty of the gauntlet while ensuring you can compete with Cynthia's Dragon powerhouse.
If you run into trouble on a specific fight, just ask. pokemon platinum nuzlocke level cap
While not a Gym Leader, this is widely considered a benchmark boss battle. Cyrus’s team is fast, aggressive, and fully evolved. His Houndoom, Honchkrow, and Gyarados can sweep an unprepared team, and his ace Crobat boasts blistering speed. The progressive cap (Level 59, but with Rare