These quests give experience rewards that are a percentage of your next level and have no upper cap (or a very high cap, at least 50 million xp).

Name Min Lvl % XP Max XP Timer
Colosseum 1+ 2% to 70% 328 Mill 1 hour
Deathtail 1+ 50% 100 Mil 3 days
Bobo's Medicine 80+ 6.67% 226 Mil 12 days
Sepulcher of Nightmares 90+ 20% 675 Mil 21 days
Hermit's Death Wish 150+ ?? 99 Mil 14 days
Lalalas in My Head 150+ 30% 710 Mil 13 days