After climbing with Nasus from D2 to Masters 296 LP with ~205 games playing top and mid lane I made a matchup tierlist based on my experience : r/nasusmains
Olaf Wild Rift Counter: Champions & Tips - Wildriftcounter
Gragas counters, stats & builds - League of Legends - SR
Gragas Counters - Best Counter Picking Stats and Matchups for LoL Patch 13.23
Gragas Counters, Builds and more - League of Legends GURU
My favorite match up: Jayce 😏 - YouTube
Gragas Build Guides :: League of Legends Strategy Builds, Runes and Items