Get 2000 combo on any difficulty ranked map, osu!standard mode only! If map is too long, you can get 2k combo and afk with NF mod.

Yoko Ishida - paraparaMAX I AR5, 2.8 stars, 36 minutes long
positive MAD-crew - Mynarco Addiction AR9, 4.8 stars, 5 minutes long
more marathon maps here (check max combo on global rankings)