no legitimate, verified, or widely recognized mod or tool

However, after checking available authoritative sources and common knowledge bases (including Minecraft modding communities, cheat client forums, and game modification documentation), exists under that exact name.

Reduce Horizontal/Vertical KB

: Players can often adjust values from 0 to 100% to fine-tune how much they move when struck.

legit game mechanics

If you want to reduce knockback without getting banned, you should focus on used by pro players in 1.8.9:

legitimate and interesting technical content

However, I can offer you related to knockback mechanics and modifications in general: