1. Low-to-Medium Overdrive*
*This made the Klon different, as the 80s-90s trend was big-loud-heavy overdrive
2. Transparent lower end with a "sweet spot" on breakup
3. (Magical) germanium diodes
4. Mythical figure box art (sigh)
Not willing to spend over 2.5k on a used Klon? There are hundreds of variants, and most range within 95% to 99.9999999% as good as a Klon. That 000000001% is perception anyhow.
Try the following (very very good) variants.